Tellabs 251 User manual

7te11abs

technical

manual

76-81251

rev B

practice

section

81251

©Tellabs, Inc., 2

November

1982

all

ri9hts

reserved,

printed

USA

251

24-Channel Digital Echo Canceller System

figure

251 24-Channel Digital Echo Canceller System

(two Systems shown

same

Mounting Assembly)

for channel idle/busy status,

it can be controlled

from amanual control panel

from aremote control

and status interface

that

uses aserial data format

compatible with EIA standard RS-232-C.

1.02 This Practice section is revised

incorporate

the information formerly contained

the 251 Practice

Supplement dated 1June 1983 and also to provide

information on

two

optional modules that allow the 251

System

operate on circuitswith amaximum end-path

delay of

60ms

(instead of30ms).

1.03 The 251 System is intended for use near

the

end points

digital carrier facilities characterized

appreciable end-to-end propagation delays. Echoes

from the associated near-end voice-frequency chan-

nel circuits are effectively cancelled by the 251 Sys-

tem. These echoes are caused

signal reflections

at impedance discontinuities and interface points

such as 4wire-to-2wire interfaces.

1.04 Because it is asplit-type

echo

canceller sys-

tem, one 251 is required at each end of the com-

posite circuit, and each System protects

the

opposite

end of the circuit from echoes in return-path chan-

nels. The split-type configuration makes

the

251 Sys-

tem completely insensitive

transmission delays on

intermediate carrier links and therefore allows

the

System

operate effectively regardless of

the

dura-

tion of these delays. Thus,

the

251 System is well

suited for abroad range of digital-network applica-

tions, including single-hop and double-hop satellite

circuits (whose round-trip delays are approximately

600

and 1200ms, respectively) and terrestrial circuits

where the transmission characteristics of

echo

sup-

pressors

via-net-Ioss (VNL) designs may be un-

desirable.

page

page 17

page

page 20

page

page 20

page

page 22

page

page 4

page 5

page 6

page 7

page 8

page 9

page

page 9

page 10

page

general

description

application

section

contents

section

general

network

interface

system

control

remote

control/status

interface

automatic

self-test

alarms

tone disabler option

section

installation

inspection

mounting

251 Assembly

central

office

equalizers

installer connections (general)

input-power

connections

facility (signal) connections

alarm connections

facility(signal) connections via

optional

twinax

connector

panels

remote

control/status

interface

connections

(general)

remote

control/status

interface

connections for single 251 System

remote

control/status

interface

connection

multiple 251 Systems

module insertion

initial power-on sequence

self-test

checkout

section

local

system

control

system operating parameters

channel

operating parameters

section

remote

system

control

remote interface

protocol

remote

control

commands

command

examples

section

system

circuit

description

section

module

and

system

block

diagrams

specifications

testing

and

trOUbleshooting

general

description

1.01 The 251 24-Channel Digital Echo Canceller

System (figure

is an adaptive, split-type echo-

control system

that

directly interfaces 1.544-megabit-

per-second digital carrier facilities (commonly called

facilities) at the

DS-1

level. The 251 System pro-

vides individual echo control for all

facil- 1.05 Asignal

the receive path of

any

of the

ity's voice-frequency

(VF)

channel circuits and per- channels served by the 251 System, followed by

the

forms comprehensive self-tests on its cancellation signal's echo in the transmit

(I.e.,

return) path, causes

circuitry

when

channels are idle. The 251 can operate the System

begin an adaptation process known as

as astand-alone system by monitoring

the

signaling convergence. During convergence, adigital signal-

page 1

practice

section

81251

processing

circuit

called a

convolution

processor

(one of which is provided for each channel) constructs

and stores in memory amathematical model of

the

channel's near-end transmission path (terminating

set and

interconnecting

link), and uses this model

compute

echo

estimate

for

the

channel. This echo

estimate

is then subtracted from

the

transmit-path

signal

actually remove

the

echo

from

the

signal.

1.06 When

the

transmit-path signal consists of both

echo (from

the

far-end speaker) and near-end speech,

the

251 System removes only

the

echo

signal, leav-

ing

the

speech

signal

intact

for

transmission toward

the

distant

end. Thus, parties

both

ends

can

talk

simultaneously (this is known as futJ-duplex speech

doubletalk)

without

the

choppiness

lockout

prob-

lems characteristic of

echo

suppressors. When only

the

far-end

party

is talking (one party

talking

is known

single

talk),

the

transmit signal consists entirely of

echo, which

the

251 System removes by subtracting

the

echo

estimate from

the

echo

signal. Any residual

echo, which is normally avery small amount (typically,

less than

-40dBmO),

is removed by an integral resid-

ual suppressor.

1.07 Convergence, the process of initially adapting

anear-end

echo

path, usually

takes

less than

200ms

(about two

three

syllables of speech), de-

pending upon

the

receive-path (far-end speech) signal

level. The 251 System can

adapt

to any near-end

path

with

aminimum

echo

return loss (ERL)

6dB

and amaximum end-path echo delay of

either

30ms

60ms, depending upon module selection. After con-

vergence,

the

251 System

continues

monitor

the

echo-delayand ERL characteristics ofthe near-end path.

During periodsof singletalk,

the

convolution processor

repeatedly updates its mathematical model to match

theseobservedcharacteristics. Thus,

any

change in

the

near-end path, such as aline being switched, will result

in anew end-path model

accommodate

the

changed

echo characteristics.

aresult, after achieving con-

vergence,

the

251 System performs

echo

cancellation

continuously, keeping

the

transmit path free of

echo

for

the

duration of

the

call.

1.08 Compact in size, an

entire

251 System com-

prisesonlysixTellabsType16 modules(five

modules

ifa

tone

disabler is

not

desired) and aprewired mounting

assembly, as shown in figure

Each of

these

System

components is described briefly below.

1.09 The

6953

Echo

Canceller

Power

Supply

and

Alarm

Module

derives regulated

power

for

all of

the

System's digital logic circuits from filtered, ground-

referenced

-44

-56Vdc

(nominal

-48Vdc)

input.

In addition,

the

6953

provides local minor alarm indi-

cations (via front-panel LED's) as well as relay opera-

tion

for

remote major

and

minor alarm indications

when faults of various types

(e.g.,

loss of power) occur.

These alarm indications can be manually

terminated

by depressing afront-panel

afarm

cutoff

pushbutton.

Fusing

for

the

System's input

power

is provided by a

13-ampere GMT-type fuse

conveniently

located

the

module's

front

panel.

1.10 The

6952

Echo

Canceller

Network

Interface

Module,

which is used in applications

where

maximum

end-path delays

not exceed 30ms, provides all re-

quired interfacingwith the

line(at

the

DS-1

level) and

performs all System timing functions (clock generation,

framing, and synchronization). If transmit synchroniza-

tion is lostdue

aproblem with

the

transmit-input PCM

line, ared

transmit

focaf LED on

the

front

panel lights. If

synchronization is lost at the channel bankwhose signals

are incoming

tothe

251 System(in whichcase

the

trans-

mit-input line indicates abit-2 alarm), ayellow

transmit

remote

LED lights. Asecond pair

front-panel LED's

providesidentical indications

forthe

receivechannel.

addition,

the

6952

contains

the

System's integral auto-

matic self-test subsystem

for

rapid

detection

and

iso-

lation of most System faults. With this subsystem, idle

channels

are

routinelysubjected

atest

sequence

that

on!! 251 SI/stem

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figure

Front detail

typical 251 System (Note:

Two

Systems, each containing the optional

6955

module, are

shown

the same

251

Assemby:)

page 2

practice section 81251

1.17 External connections

the

(DS-1) PCM

lines are normally made via wire-wrapping

terminal

blocks on the 251 Assembly's backplane. If desired,

however, the Assembly can be factory-equipped with

two

optional Tellabs 80-0121

Twinax

Connector

Panels

for concentric twinax connection of the

(DS-1) PCM lines

the Assembly. Each panel con-

tains four twinax connectors (Trompeter BJ77-type)

and serves one of the two Systems the Assembly can

accommodate. These panels are mounted on the

Assembly backplane via the same standoff posts

that

secure the CO equalizers; spacers provide the neces-

sary clearance between the panels and the equalizers.

means of aspecial printed-circuit backplane. As a

result,

neither

external

connections

individual

modules nor intermodule

connections

need be made.

Terminals on the backplane are provided

for

input

power and facility input and

output

connections. Two

versions of the 251 Assembly are available:

the

251A,

which mounts in a19-inch relay rack, and

the

251

which

mounts

in a23-inch relay rack. Each version

accommodates 12 modules (two complete 251 Sys-

tems)

and

occupies

four

mounting spaces

vertical

inches) in astandard relay rack.

1.16 The 251 Assembly is normally supplied with

four Tellabs

80-5078

Central

Office

Equalizer

sub-

assemblies

(two

per

251

System) factory-installed on

its backplane.These subassemblies provide the proper

amount

attenuation

limit

the

251 System's

transmit-output and receive-output signals (6 volts

peak)

no more than 3volts

peak

the

DX-1

cross-

connect

frame when

150

feet

(46

meters)

less of

cable

connects

the

251

System

the

cross-connect

frame. For

longer

cable runs,

two

direct-replacement

subassemblies that each provide less attenuation than

the 80-5078 are available. The Tellabs

9927

Equalizer

subassembly

is designed

for

cable runs of

150

450

feet

(46

137 meters), and

the

Tellabs

9928

Equalizer

sUbassembly

is designed for

cable runs of

450

650

feet

(137

198

meters).

1.13 The

6951

Echo

Canceller

Channel

Unit

Module

contains 12 independent convolution pro-

cessors and

their

associated timing-control circuitry.

Used in applications where maximum end-path delays 1.18 Although research indicates

that

voice-band

do not exceed 30ms, the 6951 performs the actual data can be transmitted

through

echo

cancellers

echo

cancellation for 12 of the

line's

channels.

without

degradation, the 251 System can, if desired,

Two 6951 modules are therefore required

every be equipped with an optional

6955

Echo

Canceller

251 System.

Tone

Disabler

Module.

This

module

is equivalent

tone

disablers used in

echo

suppressors and serves

1.14 The

6951A

Echo

Canceller

Channel

Unit

the entire

251

System, providing independent opera-

Module

is designed

for

use

place of the 6951 mod- tion

for

each

the

channels. Upon receipt of

ule in applications where maximum end-path delays nominal

2100Hz

digital disabling

tone

in any channel,

are as long as 60ms. While it is functionally similar to the

6955

causes all

echo

cancellation and residual-

the 6951, the

6951A

contains

convolution pro-

echo

suppression

cease

for

that

channel. Thus, the

cessors arranged

12 independent pal'rs, plus the,'r channel is rendered completely transparent; its trans-

associated timing and control circuitry. Each pair of

convolution processors serves 1of the

line's

mit-input PCM signals are not processed

but

simply

inserted into the correct time slots in the transmit-

channels, with 1processor of apair handling end-path output PCM bit stream. DIP

switches

the

6955's

delays of 0

30ms

and

the

other

handling end-path

delays of

60ms. Thus, as is

true

of the 6951 front panel allow each channel

be indiVidually

optioned so

that

echo

cancellation and residual-echo

module, one 6951Aserves 12 channels and, therefore, suppression

are

disabled only while

2100Hz

tone

two

6951A's are required

per

251 System. present

are disabled from the time

2100Hz

tone

1.15 The 251

Mounting

Assembly

is aTellabs received until the end

the

call (even if

tone

Type

Mounting

Shelf

that

is internally prewired by removed prior

the end of

the

call).

page 3

verifies

proper

operation of

their

convolution pro-

cessors and associated circuitry critical

echo can-

cellation. Any faults discovered result

local alarm in-

dications via an LED display on the System's control

interfacemodule.Thosefaultconditions

that

disablethe

System entirely, and

those

that do not disable the Sys-

tem but require immediate attention nonetheless, also

initiate relay operation in the

6953

module for remote

alarm indications.

1.11

The

6952A

Echo

Canceller

Network

Inter-

face

Module

is used in place of the

6952

module

applications where maximum end-path delays are as

long as 60ms. The

6952A

differsfrom the

6952

only

certain aspects of its EPROM software that allow the

6952A

operate in conjunction with

the

6951A

Channel Unit Module (see below).

New

system auto-

matic-self-test values

the 6952A's EPROM software,

for

example, ensure rapid detection and isolation of

6951A

channel failures.

1.12 The microprocessor-based

6954

Echo

Can-

celler

Control

Interface

Module

controls

and moni-

tors avariety of System functions. A

complement

six pushbuttons, seven

indicator

LED's, and an LED

window

display on

the

6954's

front

panel allows con-

trol

and

status information

for

the

System as awhole

and

for

its individual channels and subsystems

displayed

upon

demand; major and minor System

alarm indications are displayed automatically.

addi-

tion,

these

pushbuttons and LED's simplify

the

task

conditioning

the

251 System for aparticular applica-

tion

allowing both System and individual-channel

operating

modes

be programmed into memory

from

the

module's

front

panel. This memory is non-

volatile,

i.e.,

it retains all stored information in the

event of a

power

loss. Also available via

the

6954's

front

panel is manual override of most automatic Sys-

tem

control

functions. See paragraphs 2.05 through

2.13

for

details.

practice

section

81251

application

general

2.01 The 251 24-Channel Digital

Echo

Canceller

System is primarily intended

for

use on single-hop

and double-hop satellite circuits and long terrestrial

circuits with

(DS-1)

end

links. In such long-delay

circuits, the operating characteristics

conventional

echo suppressors may be objectionable,

thus

neces-

sitating the use of

echo

cancellers instead. Actually,

while the superior performance

the

251 System is

most noticeable on long-delay links, its insensitivity

total intermediate delay makes it suitable

for

nearly

all applications involving digital carrier. The 251 Sys-

tem cancels

echo

by adapting

each near-end

echo

path it encounters, and it can adapt

any near-end

path with an echo return loss (ERL)

greater

than

6dB

and amaximum round-trip delay (measured between

the System's receive-output and transmit-input ports)

of either

30ms

60ms, depending upon module

selection.

2.02 Atypical application of

the

251 System is

shown

figure 3. The primary cause

echoes

re-

ceived at

the

far

end

(B)

the

4wire-to-2wire voice-

frequency

(VF)

interface,

i.e.,

the

terminating

set, at

the near end

(A).

Signal reflections at

this

interface

are heard as

echoes

the

corresponding

far-end

channel. Because it is asplit-type

echo

canceller,

the

251

System at

the

near

end

actually

protects

the

far-

end receive channels from echo, and the far-end 251

System likewise protects

the

near-end receive chan-

nels from echo. This split-type configuration provides

effective

echo

control regardless of

the

total

delay

the intermediate transmission links.

6954

Echo

Canceller

Control

Interface

Mod-

ule

(one required

per

251 System).

6955

Echo

Canceller

Tone

Disabler

Module

(one

per

251 System is optional).

Issue

6900A

Blank

Type

Module

(one

per

251

System is optional when

6955

not

used).

network

interface

2.03 The 251 System interfaces

the

digital net-

work

directly

at the

(or DS-1) level and

thus

eliminates

the

need

for

per-channel echo-control

devices on

the

associated VF circuits. At

this

inter-

face level, both the transmit and

the

receive channel

of the 251 System accommodate multiplexed

input

signals

aserial stream at 1.544 megabits

per

second with segmented 1'-"255

companded

PCM

coding. (This is the

DS·1

bipolar alternate-mark-

inversion [AMI] signal format.)

2.04 The 251 System typically operates

con-

junction

with aD-type channel

bank

adigital toll

switch. In such applications,

the

251 System is nor-

mally located between a

DX-1

cross-connect frame

the

side toward

the

far

end

(i.e.,

the

satellite side)

and

another

DX-1

frame and

the

associated channel

bank

digital switch on the side toward

the

near

end

(i.e.,

the terrestrial side). An

arrangement

this

type

is shown in figure

Cabling

between

DX-1

cross-

connect

frame and aD-type channel

bank

must be

page

1.19 For any 251 System that does not require the

optional

6955

module, the Issue 2version of the

6900A

Blank

Type

Module

(Tellabs part number

826900A), which is also optional, can be used in place

of the

6955

to fill the empty module position

the

251 Assembly. The

6900A

helps

keep foreign mat-

ter

out

of the Assembly and also gives the System a

more attractive appearance.

addition, the Issue 2

version of the

6900A

can be used

silence external

alarms caused by removal of the System's

6953

mod-

ule from the Assembly. When the Issue 2

6900A

inserted into the module position from which a

6953

has been removed, aprojection at the end of the

6900A's

"pseudo

printed circuit board" opens the cut-

through module

connector

at that module position.

This causes both major-alarm and minor-alarm indica-

tions

cease. This feature is valuabie not only during

testing but also during installation of 251 Systems

prewired bays, in which case unwanted alarms can

result from module positions not yet equipped.

1.20 For reference purposes, the 251-System com-

ponents described above are summarized as follows:

251A

Mountin9

Assembly.

Twelve module posi-

tions, 19-inchrackmounting,equippedwith printed-

circuit backplane. Houses two complete 251 Sys-

temsand isfactory-equipped withfour

80-5078

Equalizer subassemblies(two per System).

*251 B

Mounting

Assembly.

Same as 251A except

23-inch rack mounting.

80-5078

Equalizer

subassembly

for

less

than

150

feet

(46 meters) of cable. Standard

equipment factory-installed on

251

Assembly

(four

80-5078's

per

Assembly).

9927

Equalizer

subassembly

for

150

450

feet (46

137 meters) of cable. Optional direct

replacement

for

80-5078.

9928

Equalizer

subassembly

for

450

650

feet

(137

198

meters) of cable. Optional direct

replacement

for

80-5078.

*80-0121

Twinax

Connector

Panels for concen-

tric

twinax connection of

(DS-1) PCM lines

251 Assembly. Optional, factory installed (two

per

Assembly).

*6951

Echo

Canceller

Channel

Unit

Module.

Serves 12 channels

applictions where max-

imum end-path delays do not exceed

30ms

(two

6951's required

per

251 System).

*6951A

Echo

Canceller

Channel

Unit

Module.

Takesthe place ofthe6951 andserves 12 channels

applications where maximum end-path delays

are as long as

60ms

(two 6951A's required

per

251 System).

6952

Echo

Canceller

Network

Interface

Mod-

ule. Used

applications where maximum end-

path delays do not exceed

30ms

(one required

per

251 System).

6952A

Echo

Canceller

Network

Interface

Mod-

ule. Takes the place of the

6952

applications

where maximum end-path delays are as long as

60ms

(one required per 251 System).

6953

Echo

Canceller

Power

Supply

and

Alarm

Module.

Operates from nominal

-48Vdc

input

(one

6953

required

per

251 System).

practice

section 81251

FAA

EHO(81

XMT XMT

OUT

251

XMTT1

LINE

24-CHAHNEil

ECHO

CANC:ELLEfIt

CHANNEL

SYSTEM

BANK

DlQITAL

SWITCH

RCVn

LINE B

SHORTiEND-PATH DIGITALCAARIER CIFlCUllS

NEAA·ENDVOICE·FREQUENCY

CIACUITS110F24CHANNEUit

\L-------------""DIG;;<;n

Al".nE1WO=ORvK

---'

130mB

MAXI"'UM)

2WtRE

TERM

@HO

XMT

SET

PAnt

4WIA£

F-1

XMTT1

LINE

2.,

24·C"AHHEL

ECHO

CANCELLeR

DIGITAL

SYSTEM

WITlI6951A'll

$WITCW

ANDIQS2A

DATER

2WIRE

TERM

@HO

4WI'RE

SET

PAnt

I~cv

i::c

RCVT1

LINE

OUT

LONG

END-PAlH A)

(8Oms

MAXIMU".

NEAR

END

(A)

figure

Typical application

251 System

ROM

END

UITS

XMT

OUT

DS-'

251

24-CHANNEL

ECHO

OX-,

CANCELLER

DX-'

SYSTEM OR

TO/F

DSX-' DSX-'

FAR-

X-CONN. X-CONN. CIRC

FRAME

RCVOUT

tRCV

DS-'

XMT

DS-' (

)

OOTYPE

CHANNEL

BANK

DIGITAL

SWITCH

TO/FROM

NEAR-END

CIRCUITS

2.06 The 251 System uses

the

basic

03-channel-

bank sequential channel-numbering scheme. With

this scheme,

the

channel

number

assigned

each of

the

T1-line (DS-1)

time

slots

the

same as

the

number of

the

time slot. Other types of channel banks,

however, use different channel-numbering schemes.

Table 1lists

the

channel-numbering

schemes

for

01 D

and

as well as

channel banks.

figure

Physical

connection

251 System

done

with

22-gauge

heavier

shielded

cable. With programmed via

the

6954

include

(1)

selection

the

22-gauge

cable, maximum

permissible

distance

be- data

transfer

rate (see paragraph 4.04)

for

the

remote

tween

the

DX-1

cross-connect

frame and

the

251

control/status

interface port,

(2)

automatic

blanking

System, including intraframe cabling in

the

DX-1

the

channel

display

after

a1-minute timeout, (3)

frame, is

650

feet

(198 meters). Where

this

distance

assignment of aSystem

unit

number

for

multiple

restriction

cannot

be met, heavier

cable

should

daisy-chained Systems, and (4) selection of one

six

used. In

extreme

cases, an intraoffice span

(Le.,

an in-

consecutive

self-test failures before

generation

of an

traoffice

repeater

line) can

used. In all applica- alarm.

tions,

separate

input and

output

cables must be used

between

DX-1

frames and

the

251 System.

system control

2.05 All

internal

System

control

functions

originate

in,

and all externally derived System

control

functions

are

handled through,

the

6954

Control Interface Mod-

ule.

Pushbutton

switches and LED's on

the

6954's

front

panel (see figure 2) provide

the

means

for

pro-

gramming

both

System and individual-channel oper-

ating

parameters

(in effect, optioning

the

System for 2.07 For each of

the

251 System's

channels, a

its

particular

application). These

codes

are

stored in a

number

control

inputs can be

entered

externally

special nonvolatile memory

that

retains all stored in-

(Le.,

via

the

6954's

front panel

via aremote

control!

formation

even if

power

the

251 System fails. After

status

interface [see paragraphs 2.11 and 2.12])

the

desired operating parameters are programmed, override certain internal

control

functions

normally

the

6954's

push

buttons

and LED's can be used to performed by

the

6954

in response

information

display

the

status

these

parameters

any time. contained in

the

transmit-input bit stream. As is

true

Specifically,

the

channe'

LED

window

and advance of all user-programmed System parameters, the status

pushbutton

are used

select

and display

the

chan- of each externally

inputted

control

function

can be

nel number, and the five control

and

two status

LED's

displayed at any time after the function

initiated.

indicate

the

selected

channel's status. The five push- The external control inputs

that

can be

entered

for

buttons

associated

with

the

control

LED's are used

each channel individually

override internal

control

the

indicated

functions.

Options

that

can be functions are as follows:

page

practice

section

81251

to hold its current contents. The

channel's

echo-

cancellation circuitry

and

residual

suppressor

still

operate normally, but the channel's convolution

processor(s) is prevented from adapting

changes in the end path.

Note:

self-testing is taking

place

the time the

Hhold

input

is entered, self-test failure

occurs

and

the 6954's

test

fail LED

lights

because adap-

tation is disabled

the Hhold input.

remote

control/status

interface

2.11 The 251 System can, if desired, be

controlled

from aremote location via a

remote

control/status

interface that uses aserial data

format

compatible

with EtA standard RS-232-C. The 251 System itself is

data terminal equipment (DTE), and

the

signals it pro-

vides are suitable

for

serial interface

with

either

data

communication equipment (DGE) or,

anull-modem

adapter is provided, with other

DTE.

All channel-related

control functions and status indications available via

the

6954

module's front-panel

switches

and LED dis-

plays are also available via

the

remote

control/status

interface.

2.10 For details on local configuration and status-

monitoring via the

6954

module's

controls

and indica-

tors, refer

section 4

this

Practice,

local

system

control.

2.08 For each channel, additional status informa-

tion derived from the

6954

module's internal control

circuits can also be displayed at any time via the

6954's

status LED's. This information consists of the

follOWing:

Channel's failure of self-test and subsequent re-

moval of the channel from service (status test fail

LED lighted).

Channel's

echo

cancellation disabled

for

any

the following reasons (status bypass LED lighted):

(1)

The channel is bypassed.

(2) The Hreset control input is activated

for

the

channel.

(3)

The channel is idle (on-hook) and therefore

has been automatically placed in

the

self-test

mode.

(4)

Atone-generated data-disable condition is

detected by the

6955

module,thuscausing

the

6954

module

automatically

generate

an H

reset control input for the channel.

2.09 When operating as astand-alone unit,

the

251

System monitors the channel-associated signal-

ing in

the

frame-6 and frame-12 signaling bits of both

the transmit and receive digital lines

determine

the

busy/idle

status of each channel. If desired (or if

channel-associated signaling is not present),

the

channel busy/idle status can be provided

externally

through the remote

control/status

interface, typically

from aprocessor-controlled toll switch (see para-

graphs

2.11

through 2.13).

251-System and

basic

03-bank

sequential

THine

channel-number

010

channel-

(08-11 assignments number number

time

slot (preferred) assignment assignment

11 1

2 2 13

3 3 2 1

,,14

5535

6615

7 7 ,9

8 8 16 15

9 9 53

10 10 17 19

11 11

12 12 18 23

"14 19 14

15 15

8 2

20 18

17 96

18 18

19 10

20 22 16

23 23

24 24 24

table

Channel-number assignments for T1-line

(OS-I) time slots

Bypass.

When

the

bypass

input

is entered, can-

cellation is disabled; the channel is routed around

the processing circuits and placed

the

self-test

mode. Self-test failures cause the

6953's

minor-

alarm relay

operate and

minor

alarm LED

light and also cause the

6954's

test

fail LED

light. The bypass input also lights

the

6954's

control

bypass and status bypass LED's.

Off

Hook.

When the

011

hook

input

is entered,

the

channel is placed in a

permanent

busy condi-

tion.

Continuous

echo cancellation takes place,

and self-testing is inhibited. Also, any existing test

fail and

minor

alarm indications

for

the channel

are cleared.

Bypass

plus

Off

Hook.

When abypass and an

011

hook

input are entered simultaneously, the

channel is completely removed from service. It is

routed around

the

processing circuits,

and

the

test fail and

minor

alarm indications

for

the

channel are cleared and inhibited.

Canceller

Only. When the canceller

only

input is

entered, the channel's residual suppressor is dis-

abled but its cancellation circuitry remains active.

Note:

self-testing is taking place

the time the

canceller

only

input

is entered, self-test failure

occurs

and

the 6954's test fail LED lights because

the residual

suppressor

checked

self-test.

HReset. When the Hreset input is entered, the H

the end-path impluse response) is zeroed, effec-

tively disabling echo cancellation

for

the channel.

The

Hreset input also lights the

6954's

status by-

pass LED.

Note:

self-testing is taking

place

the time the

Hreset

input

is entered, self-test failure

occurs

and

the 6954's test fail LED lights because can- 2.12 Figure 5shows

four

possible

remote

control/

cellation is

disabled

the Hreset input. status interface configurations.

configuration a,

Hold.

When the H

hold

input is entered, up- the control

center

is close enough

the

251 System

dates are inhibited so that the Hregister is forced to allow a

direct

RS-232-C connection. The maximum

page 6

practice

section

81251

OCE

da'sy-chain

...--

~b-Ie

(see flgure

251

SYSTEM

TERMINAL

COMPUTER

IOTEI

OTE

d,aisyot::h8in

+---c",ble

('See

figure-

r-------,

I I

TERMINAL

OR I

ICOMPUTER I

IOTEI

i--------l

I I

TERMINAL

ICOMPUTER I

IOTE)

I I

L_~TROL~~_~

+--..null modem

adapter

lsee figure til

standard

~S232C

eable

1------1

I I

TERMINAL

ICOMPUTER I

(OTEI

I I

L_~~CENTER_

251

Sy$lem

data

RS-232-C

nuU-modem Wiring

terminal

interface equipment

(OTE) (OTEf

25D 25D

signal connector connl;l!ctOf

s~gnal

FRAME

FRAM

GND GND

Jlrome

TXD

2ground 2

TXD

RXD

RTS

t:J

RTS

CTS

GND

OCD

ls.gna,

DCD

'='

ground

DTR

figure

Four

remote

control/status

interface configurations

data

link

are used

link

the

251 System

acontrol

center

located beyond the range of adirect RS-232-C

connection.

configuration c, four

251

Systems are

interfaced

with

the

control

center

via a

OTE

daisy-

chain cable (figure

7).

in configuration

the

range of

the

direct daisy-chained

connection

feet. In configuration d, the 251 Systems are inter-

faced

with

the

control

center

via a

OCE

daisy-chain

cable

(figure

8),

two

modems, and aprivate data link.

Contact

Tellabs' Applications Engineering Group

our

U.S.

Canadian headquarters

your

Tellabs

Regional Office

for

details on

other

special

interface

configurations.

2.13 For details on

the

remote

control/status

inter-

face protocol and on remote configuration and status-

monitoring procedures, refer

section

5of this Prac-

tice, remote system control.

automatic

self-test

2.14 The 251 System's self-test subsystem auto-

matically verifies proper operation of each channel's

convolution processor (and associated

support

cir-

cuits),

doubletalk

detector, and

update

control ci

figure

Null-modem wiring for connection to DTE cuits. The self-test

sequence

initiated

the

6954

recommended

range

for

direct

RS-232-C connec- Control Interface Module, which scans each channel

tion

50 feet. Anull-modem adapter, the wiring

regular 36ms intervals for on-hook/off-hook status.

which is shown in figure

interfaces

the

251 Sys- On-hook (idle) channels are marked available

for

test,

tern

(OlE)

with

the

control-center

terminal or com- and this information is passed to

the

6952

6952A

puter.

configuration b, two modems and aprivate Network Interface Module, which contains

the

self-

page 7

practice

section

81251

251 System 1RTS

251

System 2

RTS

CTS CTS

Rxe

TXD

GND

oeD

OTR

Rxe

TXD

GNP

oeD

OTR 5

1 3 278

remote control male

center

(PTE)

-connectors -

pin no

.•

FRAME

GROUND

TXQ

Rxe 3

RTS 4:J

CTS 5

GNP

OeD 8

DTR

tfemale

251

System N(up

32) RTS 0

CTS

AXe

TXD

GND DCD OTR 5

13 2 78

connector

figure

Daisy-chain

connection

multiple

251

Systems

DTE

251

System 1RTS

t:)

251

SyS1lml

2RTS

CTS CTS

Rxe

TXD

GND OCD OTR

Rxe

TXD GND DCD

OTR

1 3 278

modem

(DeE)

••

connectors-

pinno.~

FRAME

GROUND

TXO

t><:

Rxe

RTS 4

eSR 6

I--

GND

oeD

PTR

20 L.

251

System

(up

32)

RTS

CTS

RXO

TXD

GND

oCD

DTR

1327820

figure

Daisy-chain connection

multiple

251

Sysfems to

DeE

test

circuitry

and performs the actual testing. The test-

ing sequence, which takes approximately

750

milli-

seconds

per

channel, is halted

for

any channel that

goes off-hook during testing, while on-hook channels

continue

under

test until

the

end of the test sequence.

Test results are reported

for

only those channels that

have undergone

the

entire test sequence. Any chan-

nel that repeatedly fails aself-test activates aminor

alarm (see paragraphs 2.15 and 2.16) and causes a

channel alarm code

appear

the LED display on

the

6954

module.

alarms

2.15 When fault conditions are

detected

the

251 System, they are automatically classified as

minor

major, depending upon

their

effect

the

System. Both classes of alarms result in similar alarm

indications: lighting

the sysfem alarms

minor

major

LED on

the

front panel

the

6953

Power Sup-

ply and Alarm Module and lighting of

the

channel

LED display (indicating

the

affected

channel) and ap-

propriate

status

LED's on

the

front

panel of

the

6954

Control

Interface

Module. In addition,

each

the

two

alarm classes has

two

dedicated

pairs

form-C relay

contacts, both

which provide aclosure

for

an ex-

ternal indication (audible, visible,

both) when an

alarm occurs.

2.16

Minor

alarms are

generated

upon failures

single channels.

addition

initiating

the

afore-

mentioned LED indications and minor-alarm relay-

contact operation, failure

asingle channel causes

the

251 System

bypass

that

channel

that trans-

mission can still take place over

the

channel, albeit

with possible echo.

page 8

2.17 Major alarms comprise

the

following:

Loss of remote transmit or receive frame syn-

chronization (yellow transmit remote

receive

6952

6952A

module lighted). If frame syn-

chronization cannot be achieved in

3ms

less,

the aforementioned LED indications on the

6953

and

6954

modules are provided and major-alarm

relay-contact closure takes place. Also, the entire

251 System is bypassed so that transmission can

still take place over all

channels, albeit with

possible echo.

Loss

remote transmit

receive frame syn-

chronization (yellow transmit remote

receive

remote LED on

6952

6952A

module lighted). If

remote frame synchronization cannot be achieved

in the amount of time allotted,

i.e.,

if abit-2 aiarm

from

the

channel

bank

on the transmit-input or

receive-input line is detected, the aforementioned

LED indications on the

6953

and

6954

modules

are provided and major-alarm relay-contact closure

takes place. Also, the entire 251 System is

by-

passed

that

transmission can still take

ace

over all

channels, albeit with possibie echo.

Failure of 251-Assembly

input

power, faiiure of

the

6953's

power supply,

biowing of the 6953's

input-power fuse. If input power

the

251

Assem-

bly fails, if the 6953's power supply fails entirely or

cannot maintain System power within its regulated

limits,

the

6953's

front-panel 1V3-ampere fuse

blows,

the

power

LED on

the

6953

goes

off and

major-alarm relay-contact ciosure takes place.

(No

other

LED indications are provided.)

Failure of

the

6954's

microprocessor system. If

the

6954's

microprocessor system fails, the afore-

mentioned LED indications on the

6953

and

6954

modules are provided and major-alarm relay-con-

tact

closure takes place. Also, the entire 251 Sys-

tem is bypassed

that transmission can still

take place over all

channels, albeit with pos-

sible echo.

2.18 When

either

aminor

major alarm

not

caused

power

failure,

blown

fuse,

re-

moval

the

6953

from

its

module

position

occurs,

momentarily depressing the alarm

cutotf

pushbutton

the

6953's

front panel restores

the

corresponding

alarm relay

its normal state,

thereby

causing the

external alarm indications

cease. Aithough de-

pressing

the

6953's

alarm

cutoff

pushbutton clears

all external alarm indications, local alarm indications

(the lighted system alarms

major

minor

LED on the

6953

and

the

lighted LED display on

the

6954)

remain until the fault is cleared.

2.19 When

alarm caused by failure of input

power

the

251 Assembly, failure of the

6953's

power

supply, blowing of

the

6953's

input-powerfuse,

removal of the

6953

from its module position

occurs, the aiarm indications can only be cleared by

locating and correcting

the

problem.

tone

disabler

option

2.20 Should disabling of any of

the

251

System's

channels during voice-band data transmission be

deemed

necessary, the System can be equipped withpage 9

practice section 81251

an optional

6955

Echo Canceller Tone Disabler Mod-

ule. This single module serves

the

entire System, pro-

viding independent operation

for

each channel. Upon

detection in achannel of digital

2010

2240Hz

dis-

abling

tone

(at alevel greater than

-36dBmO)

either

both d'"ections of transmission, the module

disables that channel's echo-cancellation circuitry

and residual suppressor

that

the channel is com-

pletely transparent

all transmission. Aguard band

is used

prevent false operation of

the

6955

mod-

ule by

speech

signals. Three 8-position DIP switches

on the

6955's

front panel allow each channel

individually optioned so that disabling occurs only

while

tone

is present or so that disabling lasts from

the time

tone

detected

until the end

the call

(even if

tone

is removed

prior

the

end

of the call).

installation

inspection

3.01 Each component of the 251 24-Channel Echo

CancellerSystem,

i.e.,

all five modules(six ifthe

6955

used) and the

251

Mounting Assembly, should bevisu-

ally inspected upon arrival

find possible damage in-

curred during shipment. If damage is noted, aclaim

should immediately be filed with

the

carrier. If stored,

both the modulesandthe assemblyshou

beinspected

again prior

installation.

mounting

251

Assembly

3.02 The 251 AMountingAssemblymounts

astan-

dard 19-inchrelayrack, andthe251 B

Mounting

Assem-

bly mounts

astandard23-inchrelayrack. Each version

the

251 Assembly occupies 7inches of vertical rack

space. Ensure thatthe

251

Assembly is securelymount-

ed before proceeding to

central

office

equalizers and

installer connections below.

central

office

equalizers

3.03 The

251

Assembly is normallyshippedwith four

Tellabs80-5078Central OfficeEqualizersubassemblies

(one

for

the transmit

output

line and

one

for

the re-

ceive

output

line of each of the two Systemsthat the

Assembly can house) factory-installed on the Assem-

bly's backplane.

replace any of

these

equalizers

(e.g.,

if aTellabs

9927

CO Equalizer subassembly [for

150

450

feet

of cable between the System and the

DX-1

cross-connect frame) or aTellabs

9928

CO Equal-

izer subassembly [for more than

450

feet

of cable be-

tween the System and the

DX-1

cross-connect frame)

is to be used

place of an

80-5078

subassembly),

proceed as follows:

Remove and save the two Phillips-head screws

that secure the subassembly to its standoff posts

on the backplane. (If your

251

Assembly is

equipped with optional Tellabs 80-0121 Twinax

Connector Panels, remove and save the

four

Phillips-head screws that secure the twinax con-

nector panel covering the subassembly to be

replaced. Then remove and save not only the

panel itself but also the four spacers between the

panel and the subassemblies below

it.)

Unplug the subassembly

be replaced from its

five-pin

connector

(P4,

P5,

PIG, or

I).

Plug the new subassembly into the five-pin con-

nector.

practice

section

81251

and

two

25-pin

female

RS-232-C

connectors.

These

items

are

shown

figure

and

all

mandatory

and

optional

connections

asingle 251 System

are

sum-

marized

table

Detailed

wiring

instructions

and

complete

wiring

table

for

both

systems

in a251

Assembly

not

equ

ipped

with

twinax

connector

pan-

els

paragraphs

3.07

through

3.09. If

your

251

Assembly is

equipped

with

twinax

connector

panels,

make

all

connections

except

facility

(signai)

connec-

tions

and cable-shield

connections

directed

paragraphs 3.07

through

3.09;

then

proceed

para-

graph

3.10.

Note:

Before

making

any

connections

the

251

Mounting

Assembly,

ensure

that

power

off

and

modutes are

removed.

Modules

shoutd

inserted

into

their

Assembly

positions

onty

after

all

wiring is

completed. For easy reference

during

the wiring

pro-

cedure, table 3lists each

individual

connection

(both

mandatory

and

optional)

for

each

the

two

251 Sys-

tems

that

can

housed

in a251 Assembly. Acheck-

list

in the table's

rightmost

column

can

be filled

out

mandatory

connections:

power

inputs:

-BAT

(-44

to -56Vdc, filtered,

positive

ground

referenced)

+GND (input ground

[OVdc))

lines

(05-1

message

signals}(see

note

1):

ReV

IN T&R (receive input from far end)

ReV

OUT

T&R (receive

output

to near end)

XMT

IN T&R (transmit input from near

end)

XMT

OUT

T&R

(processed transmit output to far

end)

optional

connections:

power

inputs:

FRAME

GROUND

lines

(05-1

message

signals)

(see note

1):

RCV

(receive input cable shield)

ReV

OUT

(receive output cable shield)

XMT

(transmit input cable shield)

XMT

OUT

(transmit output cable shield)

alarm

outputs:

MINOR ALARM (Two form-C sets

minor-alarm relay

contacts

are

available)

MAJOR ALARM (Two form-C sets

major-alarm relay

contacts

are

available.)

remote

control/status

interface

connections

(made

via

25-pin

o-subminiature

RS-232-CIV.24 connector)

(see

note

2):

FRAME

GROUND

TXD

(transmit data output)

RXD

(receive data input)

RTS

(request to

send)

CTS

(clear to

send)

GND

(signal ground)

DCD (data

carrier

detect)

DTR

(data terminal ready)

Note

1: These

connections

can be made

either

directly

to the

251-Assembly

backplane

via wire-wrapping or to an

optional

Teflabs 80-0121 Twinax

Connector

Panel via

appropriate

cables.

Note

2: The

251

System's

remote

control/status

interface sig-

nals are

compatible

with EIA

standard

RS-232-C

electrical

characteristicS

and

are thus suitable

for

serial

interface

with

data

communication

equipment.

Secure

the

new

subassembly

its

standoff

posts

with

the

two

Phillips-head screws. (If

your

251

Assembly

equipped

with

twinax

connector

pan-

els,

replace

the

four

spacers

between

the

two

subassemblies

and

the

twinax

connector

panel

that

was

removed, reinstall

the

panel

over

the

subassemblies, and

secure

the

panel and sub-

assemblies

with

the

four

Phillips-head screws.)

installer

connections

(general)

3.04

Because

the

251

Assembly

prewired and

equipped

with aprinted-circuit backplane,

neither

ex-

ternal

connections

individual

modules

nor

intermod-

ule

connections

need

be made.

The

only

mandatory

external

connections

each 251

System

in a251

Assembly

are

follows:

Eight

facility

(signal)

connections,

consisting

one

tip

and

one

ring

connection

for

each

the

four

inpul/output

cables

accessing

the

System.

Unless

the

251

Assembly

equipped

with op-

tional

twinax

connector

panels (see paragraph

3.10),

these

connections

are

made

via wire-

wrapping

four

clearly

labeled

three-pin

terminal

blocks

the

Assembly's backplane.

Input

battery

and

ground

connections,

which

are

made

with

16AWG

heavier

wire

screw-type

terminals

on a

three-position

barrier

strip

the

Assembly's backplane.

3.05

Optional

external

connections

each 251

System

in a251

Assembly

comprise

the

following:

One

cable-shield

connection

for

each

the

four

facility

(signal)

inpul/output

cables. Unless

the

251

Assembly

equipped

with

optional

twinax

connector

panels

(see

paragraph

3.10),

these

are

made

via

wire-wrapping

the

same

three-pin

ter-

minal

blocks

used

for

facility

(signal) connections.

Input-power

frame

ground.

This

connection

made

with

16AWG

heavier

wire

the

same

three-position

barrier

strip

used

for

input

battery

and

ground

connections.

Connections

for

external

minor-alarm indications.

These

connections

are

made

via

wire-wrapping

asix-pin

terminal

block

the

251 Assembly's

backplane.

(Two

sets

minor-alarm relay con-

tacts

are

provided,

and

three

pins

are

used

for

each

set.)

Connections

for

external

major-alarm indications.

These

connections

are

made

via

wire-wrapping

asix-pin

terminal

block

the

251 Assembly's

backplane.

(Two

sets

major-alarm relay

con-

tacts

are

provided,

and

three

pins

are

used

for

each

set.)

Remote

controllstatus

interface

connections.

These

connections

are

made

via a

25-pin

female

D-subminiature

connector

arranged

for

RS-232-C

serial

interface

and

located

the

251 Assem-

bly's backplane.

3.06

Because

the

251

Assembly

can

house

two

separate

and

independent

251 Systems,

the

Assem-

bly's

backplane

contains

two

input-power

barrier strips,

two

sets

wire-wrapping

terminal

blocks

for

facility

(signal), minor-alarm,

and

major-alarm

connections,

page

table

Summary

mandatory

and

optional external

connections

251

System (made via

251-Assembly backplane)

practice

section

81251

(by checking the appropriate boxes) either prior to

wiring

indicate

the

required

connections

for apar-

ticular

application

wiring is

being

done

pro-

vide a

record

for

future reference.

input-power connections

3.07

Input-power

connections

each

251

System

the

251

Assembly

must

made

with

16AWG

heavier

wire.

The

screw

terminals

the

three-posi-

tion

input-power

barrier

strips

to"

12AWG

wire

directly;

wire

terminated

appropriately

sized

spade

lugs

can

also

used.

Make

the

input-power

connections

the

251

Assembly

follows:

for righthand system

(as

viewed

from front

assembly):

Connect

fiitered,

positive-ground-referenced

-44

-56Vdc

input

power

the

-BAT

terminal

barrier

strip. terminal

section

block, or terminal

pin check-

system system connection connector no. designation or no.

list

righthand power inputs input battery

(-44

-BAT

(as

viewed

-56Vdc,

filtered,

from

front

positive ground referenced)

251

input ground (positive)

+GND

Assembly)

frame

ground*

FRAME

lines

(D5-1

receive input tip

RX IN T(TIP)

message signals) from

far

ring

RX IN R(RING)

end

shield*

RX IN

(SHIELD)

receive

output

tip

OUT

T(TIP)

near

ring

OUT

R(RING)

end

shield

OUT

(SHIELD)

transmit input tip

IN T(TIP)

from near ring

IN R(RING)

end

shield*

(SHIELD)

processed

tip

DUT

T(TIP)

transmit Qut-

ring

DUT

R(RING)

put

far end shield* pg

OUT

(SHIELD)

minor alarm first

set

normally Pl (upper MIN

outputs relay con- dosed three

pins)

tacts* common MIN C

normally MIN NO

open

second

set

normally Pl (lower MIN

relay

closed

three pins)

contacts* common

MINC

normally MIN

open

major alarm first

set

normally

(upper MAJ

outputs relay con-

closed

three pins)

tacts

*common

MAJC

normally

MAJNO

open

second

set

normally

(lower MAJ

of relay

closed

three

pins)

contacts* common

MAJC

normally MAJ

open

remote control/ FRAME GROUND 25-pin connector 1

status

inter-

TXD

(transmit data output) J15 (REMOTE 2I

face*t

RXD

(receive data input) CONTROL RS-232/ 3

numbers on

RTS

(request

send)

V.24 DTE) 4connector.J15

CTS

(clear

send)

5listed

for

GND

(signal

ground) 7reference only

DCD

(data carrier detect) 8

DTR (data terminal readyI20

continued on next

page

table 3. Wiring table: external connections to

251

Assemblybackplane

tor

righthand

and

lefthand

251

Systems

Assembly

page

practice

section

81251

barrier

strip. terminal

section

block,

terminal

pin check-

system system connection connector no. designation or

no.

list

lefthand power inputs input battery

1-44

P18

-8AT

(as

viewed

-56Vdc,

filtered,

from front positive ground referenced)

251

input

ground (positive)

P18

+GND

Assembly) frame

ground*

P18

FRAME

lines

IDS-1

receive

input

tip

P13

RX IN T(TIP)

message signals) from

far

ring

P13

RX IN R(RING)

end

shield

P13

RX IN

(SHIELD)

receive output

tip

P12 RX OUT T(TIP)

near

ring

P12

RXOUT

R(RING)

end

shield"

P12

RXOUTSH

(SHIELD

transmit input

tip

P14

IN T(TIP)

from

near

ring

P14

IN R(RING)

end

shield*

P14

(SHIELD)

processed

tip

P15

OUT

T(TIP)

transmit Qut-

ring

P15

OUT R(RING)

put

far

end shield*

P15

OUT

(SHIELD)

minor alarm first set

normally

P17

(upper MIN

outputs relay con- closed three pins)

tacts*

common

MINC

normally MIN

open

second set

normally

P17

(lower

MIN

relay closed three pins)

contacts* common

MINC

normally

MIN

open

major alarm first set

normally

P16 (upper MAJ

outputs relay Con- closed three pins)

tacts* common MAJ C

normally

MAJNO

open

second set normally

P16

(lower

MAJNC

relay closed three pins)

contacts* common

MAJC

normally

MAJNO

open

remote control! FRAME GROUND 25·pin connector 1

status inter- TXD (transmit data output) J16 (REMOTE 2

face*t

RXD (receive data input) CONTROL RS-232/ 3pin numbers

RTS

(request

send)

V.24 DTE) 4connector J16

CTS

(clear

send)

5listed for

GND (signal ground) 7reference only

DCD

(data carrier detect) 8

DTR(data terminal ready) 20

*This connection or group

connections

optional.

tThe

251 System's remote control/status interface signals

are

compatible with EIA standard RS-232-C electrical character-

istics and are thus suitable for serial interface with data communication equipment (DCE).

table

Wiring table:

external

connections

to 251 Assembly

backplane

for

righthand

and

iefthand

251 Systems in Assembly

page 13

practice

section

81251

barrier strip

(located at

the

lower lelthand cor-

ner

the

assembly as viewed from

the

back).

Connect

positive ground

the

+GND

terminal

on barrier strip

P3.

Connect

optional frame

ground

(if used)

the

FRAME terminal on barrierstrip

P3.

for

lefthand

system

(as

viewed

from

front

assembly):

Repeat steps Athrough C

but

make connections

barrier strip P18 (located at

the

lower

right-

hand

corner

of the assembly as viewed from

the

back) instead of

P3.

facility

(signal)

connections

(without

twinax

connector

panels)

3.08 For each

the

two

systems the 251 Assem-

bly can house, four three-pin terminal blocks are pro-

vided on

the

Assembly's backplane

for

connection

the

1.544Mbps, 100-ohm PCM lines.

Connections

be-

tween the Assembly and the

DX-1

cross-connect frame

should be made with 22AWG twisted-pair shielded

cable. Separate receive input, receive output, transmit

input, and transmit

output

cables are recommended.

If cables containing multiple twisted pairs with acom-

mon shield are used, ensure

that

the

transmit input

(TX

IN) and receive input (RX IN) pairs are

adif-

ferent cable than

the

transmit

output

(TX

OUT) and

receive

output

(RX OUT) pairs. This will prevent cross-

talk between the high-level

6V peak) regenerated

output

signals from the system and the low-level (1.5

3V peak)

input

signals. Depending upon the CO

equalizers used (see paragraph 3.03), the maximum

permissible length of 22AWG cable between the As-

sembly and the

DX-1

cross-connect frame is

650

feet

(198 meters). If

this

distance restriction cannot

be met, heavier cable must be used. In extreme cases,

an intraoffice span

(i.e.,

an intraoffice repeater line)

can be used. Make

the

facility (signal) connections

(by wire-wrapping) as follows:

Note:

accommodate awide range

office in-

stal/ation methods, the

SHIELD

wire-wrapping pins on

PCM-line terminal blocks P6 through P9

and

P12

through P15 are provided as tie points only. These

pins are

not

connected to frame

ground

(as

might

assumed due to the frame-ground symbol on the 251-

Assembly backplane adjacent to those pins). This sym-

bol

merely indicates that grounding connections may

be made,

desired,

connecting jumpers from the

SHIELD

wire-wrapping pins to the

FRAME

(frame

ground) terminals on terminal strips P3

and

P18.

The

only prewired connections to the

SHIELD

pins are as

fol/ows:

OUT

on P6 to RX

on P7

on P8 to TX

OUT

on P9

OUT

on P12 to

on P13

on P14 to

OUT

on P15

for

righthand

system

(as

viewed

from

front

assembly):

Connect

the

receive

input

tip

lead

and the receive input ring lead

Rof

terminai block

P7.

Connect

the receive

input

cable shield (il pres-

ent)

IN SH of terminal

block

P7.

Connect

the

receive

output

tip

lead

OUT

Tand the receive

output

ring lead

OUT

Rof terminal

block

P6.

Connect

the

receive

output

cable shield (if pres-

ent)

OUTSH of terminal

block

P6.

Connect

the

transmit

input

tip

lead

fN T

and

the

transmit input ring lead

terminal block

P8.

Connect

the

transmit

input

cable shield (if pres-

ent) to pin

SH of terminal

block

P8.

Connect

the

transmit

output

tip

lead

OUT Tand the transmit

output

ring lead

OUT Rof terminal

block

P9.

Connect

the

transmit

output

cable shield (it pres-

ent)

OUT

terminal

block

P9.

for

lefthand

system

(as

viewed

from

front

assembly):

Connect

the receive

input

tip

lead

fN T

and the receive input ring lead

Rof

terminal

block

P13.

Connect

the receive

input

cable shield (if pres-

ent)

terminal

block

P13.

Connect

the

receive

output

tip

lead

OUT

Tand the receive

output

ring lead

OUT

Rof terminal block P12.

Connect the receive

output

cable shield (if pres-

ent)

OUT

terminal

block

P12.

Connect

the

transmit

input

tip

lead

IN T

and

the

transmit

input

ring lead

terminal block P14.

Connect

the

transmit

input

cabie shield (if pres-

ent)

IN SH of terminal

block

P14.

Connect

the

transmit

output

lip

lead

OUT

Tand the transmit

output

ring lead

OUT Rof terminal

block

P15.

Connect

the transmit

output

cable shield (it pres-

ent)

OUT

terminal

block

P15.

alarm

connections

3.09 For each of

the

two

systems

that

can be

housed

a251 Assembly,

two

sets

minor-alarm

and

two

sets of major-alarm relay

contacts

are pro-

vided

for

external alarm indications. Each

set

of relay

contacts consists of anormally closed (NC) contact, a

common

(C)

contact, and anormally open (NO) con-

tact. Normal conditions are indicated by aclosure be-

tween the NO and Ccontacts, and alarm

conditions

are indicated by aclosure between

the

NC and C

contacts. If external alarm indications are desired,

make the

connections

(by wire-wrapping) as follows:

Note:

Before the 6953 Power

Supply

and

Alarm Mod-

ule

for

a251 System is

inserted

into

its assembly

position, alarms will be

indicated

aI/

four

sets

alarm

contacts

for

that

system.

for

righthand

system

(as

viewed

from

front

assembly):

For external minor-alarm indications, make

the

appropriate alarm-device

connections

one

both sets of NC,

and NO pins on ALARMS

MIN

terminal

block

P1.

page f4

practice

section

81251

For

external

major-alarm indications, make

the

appropriate

alarm-device

connections

one

both

sets of NC,

and NO pins on

ALARMS

MAJ

terminal

block

P2.

for

lefthand

system

(as

viewed

from

front

assembly):

For

external

minor-alarm indications,

make

the

appropriate

alarm-device

connections

one

both sets

NC,

and

pins

ALARMS

MIN

terminal

block

P17.

For

external

major-alarm indications, make

the

appropriate

alarm-device

connections

to one or

both

sets

of NC,

and NO pins on

ALARMS

MAJ

terminal

block

P16.

facility

(signal)

connctions

via

optional

twinax

can

nectar

panels

3.10 For 251 Assemblies whose backplanes are

equipped with

the

optional 80-0121 Twinax Connector

Panels (two

per

Assembly),

(OS-1) PCM facility con-

nections

each System

are

quickly and easily made

via

the

four

concentric

twinax connectors on

the

appropriate panel (see figures 10 and

11).

Make these

connections

as follows:

for

right

hand

system

(as

viewed

from

front

assembly:

Connect

the

receive input twinax cable

connec-

tor

(RX IN) on the twinax

connector

panel for

DIGITAL

ECHO

CANCELLER

SYSTEM AThis

panel is located to

the

immediate left of three-pin

terminal blocks

through

as viewed from

the

rear

the

assembly.

Connect

the

receive

output

twinax cable

con-

nector J2 (RX

OUn

the

twinax connector panel

for

DIGITAL

ECHO

CANCELLER

SYSTEM A

Connect

the

transmit input twinax cable

con-

nector

(TX IN)

the

twinax

connector

panel

for DIGITAL ECHO

CANCELLER

SYSTEM

Connect

the

transmit

output

twinax cable

con-

nector J4 (TX

OUn

on the twinax

connector

panel

for DIGITAL ECHO CANCELLER SYSTEM

for

lefthand

system

(as

viewed

from

front

assembly):

Connect the receive input twinax cable

connec·

tor

(RX IN) on

the

twinax

connector

panel for

DfGITAL ECHO CANCELLER SYSTEM

This

panel is located

the

immediate left of three-pin

terminal blocks P12 through P15 as viewed from

the

rear

the

Assembly.

Connect the receive

output

twinax cable

con-

nector

(RX

OUn

the

twinax

connector

panel

for

DIGITAL ECHO

CANCELLER

SYSTEM

Connect

the

transmit input twinax cable

con-

nector J3 (TX IN) on

the

twinax

connector

panel

for DIGITAL ECHO

CANCELLER

SYSTEM

Connect

the

transmit

output

twinax cable

con-

nector J4 (TX oun on

the

twinax

connector

panel

for DIGITAL ECHO

CANCELLER

SYSTEM

remote

control/status

interface

connections

(general)

3.11

Each of

the

two

251

Systems in a

251

As-

sembly can be optionally

controlled

via an RS-232-C

serial interface. This is

accomplished

via

one

25-pin

female D-subminiature connector for each System

the 251 Assembly's backplane. In addition,

the

251

System is

designed

that

systems can

"daisy-chained"

together

the

same cable,

thereby

minimizing

the

number

RS-232-C

ports

required

control alarge

number

of 251 Systems.

Make

the

SPACER

EQUALIZER

SUBASSEMBLY

251

ASSEMBLY

BACKPLANE

STANDOFF

POST

'-----,---'-----,~r_+_--"""""""

FACTORY-I

NSTALLED

TIP

....

RING,

AND

SHIELD

CONNECTIONS

FRuM

TWINAX

CONNECTORS

PCM·L1NE

IN,

OUT,

IN,

AND

OUT

THREE-PIN

TERMINAL

BLOCKS

(CONNECTIONS

THE

TWO

TWINAX

CONNECTORS

NOT

VISIBLE

THIS

DRAWING

ARE

ONLY

PARTIALLY

SHOWNI

TWINAX

CONNECTOR

PANEL

TWINAX

CONNECTORS

(FOUR

PER

PANEL)

figure

10.

Side view

80-0121 Twinax Connector Panel

shOWing

its installation over CO equalizersubassemblies on 251 Assembly backplane

page

practice

section

81251

twO

lnax

con

nee

pane

/Inax connee

pane

for

righthand

system

for

le"hand

system

0000

PCM

LINES

PCM LINES

OUT

looojP6

RXIN

RXOUT

100

alP12

1000

1000lp13

TX PCM

LINES

PCM

LINES

TXOUT

TXIN

TXQUT

@J @J @J

P16

J3 J4

looolP8

J3 J4

1000lp14

[ooojpg

looolP15

J1, J1.

0000

.,.

DIGITAL

ECHO

CANCELLER

SYSTEM

DIGITAL

ECHO

CANCELLER

SYSTEM

....

~----

righlhand

system

viewed

from

front

-----

...

•.

-----

le"hand

system

viewed

from

front

-------<.~I

figure

II.

251

Assemblybackplane wilh optional 80-0121 Twinax Connector Panels

(for

simplicity,

some

backplane

details

and

designations

are

omitted

and

presence

equalizer

subassemblies

under

connector panels is

not

indicated)

remote

control/status

interface

connections

the

251 Assembly as follows:

Note

Should

you require

detailed

information

single-system

and

multiple-system

(daisy-chain)

connections,

such

information

follows

these

basic

instructions.

Note

For

connection

to data terminal

equipment

(OTE),

the cable

must

contain

anull-modem adapter.

See

paragraph

3.13.

for

righthand

system

(as

viewed

from

front

assembly):

Plug an appropriate 25-pin male D-subminiature

connector

from

the

data

communication

equip-

ment (DCE)

data terminal

equipment

(DTE)

into

REMOTE CONTROL RS232/V.24 OTE

connector

JI5

the

251 Assembly's backplane.

for

lefthand

system

(as

viewed

from

front

assembly):

Plug an appropriate 25-pin male

D-subminiature

connector

from

the

data

communications

equip-

ment

(DCE)

data

terminal

equipment

(DTE)

into

REMOTE CONTROL RS232/V.24 OTE

connector

JI6

the

251 Assembly's backplane.

remote

control/status

interface

connections

for

single

251

System

3.12

Connection

DCE.

The

251 System con-

tains

the

necessary

interface

circuits

for

connections

to acustomer's data communication

equipment

(DC

E).

These connections, along

with

their

circuit

designa-

tions

and

corresponding

numbers

on each

the

251 Assembly's 25-pin

female

REMOTE CONTROL

RS232/V.24 OTE connectors, are

listed

table

connection

(signal) EtA RS·232·C

CCITTV.24

251-Assembly RS·232·C

circuit circuit

250

connector

no.

designation

protective

ground

101

(frame or earth)

transmitted data

(TXD)

103 2

received data

(RXD)

104 3

request to send

(RTS)

105 4

clear to send

(CTS)

CB 106 5

signal

ground

(common return)

102 7

received line signal detector

(DCD)

CF 109 8

data terminal ready

(DTR)

108.2

table

RS-232-C

interface

connector

assignments

page

practice section 81251

....

Orawing represents

251 Assembly

viewed from

the

FRONT.

tt t

iii

_ N

i i

..,.

.. ..

..,.

.. ..

;;

o'"

inc:.

,inN ,

;; ;;

'" '"

<0 <0

.. .. ..

....

.. ..

<0 <0 <0

Caution:

Before inserfing a6953 module into

removing a6953 module from its position in the

251

Assembly,

certain

remove

the

6953'5

front-panel

fuse

so that

power

not

applied to the

System during the module's insertion

removai.

All

other

modules may be safely inserted into

re-

moved from the 251 Assembly with

power

applied

to the System. This means that 6951

6951A

Channel Unit Modules

and

the 6954 Controi Inter-

face Module can be replaced without interrupting

transmission on the transmit

and

receive

(OS-1)

PCM lines. Only the 6953 Power Supply

and

Alarm

Module

and

the 6952

6952A Network Interface

Module need be operating for transmission con-

tinuity to exist through the

251

System.

Notes:

Please be

aware

that

the

module

ar-

rangement

different

for

each Sys-

tem

the

Assembly

and

that

the

6953

modules

occupy

the

Assembly's

first

and

twelfth

module

positions.

2.The

6955

is optional;

the

690QA Blank

Type 16

Module

(also optional) can be

used to fill the

empty

module position

the

6955

not

needed.

3.These

6951's

6951A's

serve chan-

nels 1

through

12 of

their

respective

Systems.

4.These

6951's

6951A's

serve chan-

nels

through

24 of

their

respective

Systems.

figure

12.

251-Sysfem moduie arrangement for both

Systems

251

Assembly

Doublecheck that all modules are installed

their correct positions and firmly seated

their

connectors.

Apply power

each 251 System in

the

Assembly

by reinserting

the

GMT-type fuse into its holder

the

front panel of

the

system's

6953

module.

tefth.nd system righthand system

(note

(note 1)

AssembIY~~

position 1 2 3 4 5 6 7 8 9

Insert each

6953

module into its proper Assembly

position (position 1

for

the

lefthand System, posi-

tion 12 for

the

righthand System). (By inserting

the

6953

modules first,

the

chance

installing

other

modules in the wrong positions is reduced.)

For each System

the

Assembly, insert

the

re-

maining modules into

their

proper

Assembly posi-

tions as shown in figure 12.

initial

power-on

sequence

3.16 When a251 System is initially connected

its nominal

-48Vdc

power

source,

the

6953's

power

LED should light steadily, and all

control

and status

LED's on the

6954

as well as the

major

alarm LED on

the

6953

should light briefly and

then

oft. In addi-

tion, the numbers

8.8.8.

should appear briefly in

the

6954's

channel

LED display;

the

display should then

blank

On the

6952

6952A

module, all four

page

Caution:

Before

inserting

any

modules into the

251 Assembly, remove the 1'13-ampere GMT-type

fuse from the fuse

holder

on the

front

panel

each

the two 6953 Power Supply

and

Alarm

Modules to be installed in the Assembly.

3.15 Asingle 251 System is housed

one half

(six module positions)of

the

251 Mounting Assembly.

Thus,

one

Assembly can house

two

complete

251

Systems, one in module positions 1through 6and

the

other

'In module positions 7through 12. Each

modu

the

251 System plugs physically and elec-

trically

into

connector

the

rear of its Assembly

position, and each Assembly position is dedicated

with respect

the

particular module that it houses.

Module-position assignments are clearly indicated on

the Assembly. Figure

shoWS

the mandatory module

arrangements

for

both

systems

in a251 Assembly.

Please

observe

that

the

module

arrangement

different

for

each

the

two

Systems

because

the

6953

modules

occupy

the

first

and

twelfth

mod-

ule

positions

the

Assembly

rather than the first

and seventh. This arrangement (power supplies at op-

posite ends of

the

Assembly) results

better

heat

dissipation

for

longer

component

life. Insert

the

mod-

ules for each

251

System into

the

Assembly as follows:

Ensure

ihat

the front-panel GMT-type fuse is re-

moved from each

6953

Power Supply and Alarm

Module

be used in the 251 Assembly.

Connection names and abbreviations are in accord-

ance

with

EIA standard RS-232-C. Pin numbers not

listed have

connections.

3.13

Connection

DTE. The 251 System, which

itself is

data

terminal equipment (DTE), requires anull

modem

for

connection

other

(e.g.,

acustomer's)

DTE.

The required null-modem wiring is shown in

figure 6in section 2of

this

Practice.

remote

control/status

interface

connection

multiple

251

Systems

3.14 Aspecial daisy-chain cable

with

multiple 25-

pin male RS-232-C

connectors

is required

for

remote

control/status

interface connection of multiple 251

Systems. Up

Systems can be controlled via a

single RS-232-C serial link. There are

two

types of

daisy-chain cable:

DTE

and DCE. The DTE daisy-chain

cable (see figure 7in section 2of

this

Practice) inter-

faces

the

daisy-chained 251 Systems with

DTE;

this

type of cable contains

integral null modem adapter.

The DCE daisy-chain cable (see figure 8in section 2

of this Practice) interfaces the daisy-chained

251

Sys-

tems

with

DCE. The DCE and DTE daisy-chain cables

can themselves be daisy-chained if appropriate con-

nectors

and/or

adapters are used.

Note:

the

6954

Control

Interface Module

any

251 System in adaisy-chain arrangement is removed,

shorting

contacts

the

251

Assembly

by-

pass

that

251 System in

the

daisy chain. These short-

ing

contacts

are

provided

for the RXO-to-

TXO

and

OCO-to-OTR

connections

on the 251 Assembly's 25-

female RS-232-C connectors.

module

insertion

practice

section

81251

table 5. Factory-programmed (at time

shipment

from Tellabs) 251-System parameters

4.03

Resetting

the

6954

Control

Interface

Mod-

ule.

The following procedures require

that

the

6954

module's front-panel

channel

display be

blank

before

beginning

the

procedure. To reset

the

6954

module

this state, proceed

follows:

If atwo-digit number (see note) is displayed

the

6954

module'sfront-panel

channel

display, depress

thefront-paneladvance

pushbutton

until

the

chan-

nel

display

goes

blank. Holding

the

advance push-

button depressed causes

the

displayed

number

be Incrementedapproximately4

times

per

second.

After24 is displayed,

the

increment

blanksthe

display. Resetting is

then

complete.

Note:

two-digit

number

witha

decimal

point

tothe

right

each

number

indicates

self-test

failure.

not

necessary

clear

such

indications

before

proceeding

with the

following

procedures. Proce-

dures

for

clearing

self-test

failures are

included

section

this Practice.

S. If athree-digit number

displayed in

the

channel

display, hold theH

hold

pushbuttondepressedwhile

channeloperatingparameters. The selectedparameters

are stored

aspecial nonvolatile

memory

that

retains

all storedinformationeven if

powertothe

251 Systemis

removed orfails.

Thissection

describes

the

procedures

for

programming System and individual-channel oper-

ating parameters via

the

6954

module's front panel.

Referto

paragraphs2.05 through 2.07

for

briefdescrip-

tions of the functions of

the

6954's

front-panel push-

buttons

and

displays.

system

operating

parameters

4.02 The follOWing System operating parameters

can be programmed via the

6954

module's

front

panel:

(1)

data-transfer rate for the RS-232-C remote

cantrall

status interface port, (2) display timeout,

(3)

System

unit number, and (4) number of consecutive self-test

failures before

alarm indication. Paragraphs 4.03

through 4.08 contain the procedures

for

programming

these

System operatingparameters.The251 System is

shipped from Tellabs with its parameters factory-pro-

grammed as indicated

tabie

Note.

In each

the

procedures

below.

assumed

that

only

one

System

operating

parameter

being

pro-

grammed.

more than

one

parameter

being

pro-

grammed.

refer

paragraph

4.08.

6954

parameter

selection channel

display

indication

data·transfer

rate for RS-232-C 300bps 103

remote contrail

interiace port

6954 channel display timeout

201

and

LED

timeout effect

System unit number 1301

number of self-test 3

403

failures before alarm

LED's should also light. The two red

local

LED's

should go off

after

afew seconds; the two yellow

remote LED's may, however, remain lighted for up

approximately 18 seconds before going off. If one

both of the

6952's

6952A's red

local

LED's remain

lighted for more than approximately 18 seconds, refer

section 9of this Practice for testing and trouble-

shooting information. If atwo-digit channel number

(with each digit followed by adecimal point) remains

the

6954's

channel

LED display

and/or

if any of the

6954's

control

status LED's remain lighted after the

System is initially powered up, proceed as follows;

Wait

seconds. If the

channel

display does not

clear

and

the

other

LED's do not

off automati-

cally, proceed

step

Momentarily

depress

the

advance

pushbutton

once. The

channel

display should

indicate

00 and

all lighted

control

LED's should

off. If any con-

trol

LED remains on, momentarily depress its cor-

responding

control

pushbutton

turn

it off. Pro-

ceed

step

Momentarily depress

the

advance pushbutton

times

advance

the

channel numbers from

through 24. When 24 is displayed, momentarily

depress

the

advance

pushbutton

one

more time.

The channel display should

blank. If it does

not,

and/or

if any

control

LED's

cannot

be turned

off, refer

section

9of

this

Practice

for

testing

and troubleshooting information.

self·test

checkout

3.17 If

the

channel

LED display and all

control

LED's on

the

6954

module

off

after

lighting briefly

upon

initial power-up

after

the

above steps are per-

formed, all

channels of

the

251 System pass the

automatic self-testing routine.

verify that the self-

test program functions properly, proceed as follows:

Depress the 6954's advance pushbutton

select

any desired channel (as indicated in the

channel

LED display).

Momentarily depress

the

6954's

bypass pushbut-

ton. The bypass LED should light and remain on.

Momentarily

depress the

6954's

Hreset pushbut-

ton. The Hreset LED should light and remain on.

After adelay of approximately 1minute, the

6954's

test fail LED and

the

6953's

minor

alarm

LED

should both light.

Momentarily depress

the

6954's

Hreset pushbut-

ton once again. The Hreset LED should

off im-

mediately,

and

the

6954's

test

fail LED and

the

6953's

minor

alarm LED should go

off

atter

maximum delay

approximately

seconds. If

any of

these

three LED's remain lighted, refer

section 9

this

Practice

for

testing and trouble-

shooting information.

Depress the

6954's

bypass pushbutton once again

take

the

System

out

of the bypass mode (the

bypass LED should

off).

local

system

control

4.01 Pushbutton switches and LED's on the

6954

Control InterfaceModule'sfrontpanel(figure

provide

the meansforprogramming both System and individual-page

practice section 81251

4.06

System

Unit

Number.

When

the

System is

be programmed

monitored via

the

remote

control/

status interface,aSystem unit

number

32) is

sent

address

the

desiredSystem (recall

that

multipleSys-

tems can be interfaced

one remote

interface

serial

link).

assignaSystem unitnumber,proceedasfollows:

Reset the

6954

module as described

paragraph

4.03.

8. While holding

the

hold

pushbutton

depressed,

momentarilydepresstheadvance pushbutton three

times.Then release

the

hold

pushbutton.Athree-

digit

numberwith

inthe

leftmost

positionshould

appear

in the channel display. The 3

denotes

the

third System operating parameter.

Depress

the

advance pushbutton until the desired

System unit number

(01

32) appears

the

two

rightmost digitsof

the

channel display. Holding the

advance pushbutton depressed causes the dis-

played number

be incremented approximately4

times

per

second.

Note:

FormultipleSystems daisy-chainedto asingle

remote control/status interface link, each System

must be assignedaunique System

unit

number.

Reset the

6954

moduleas described in paragraph

4.038.

4.07

Number

Self-Test

Failures

for

Alarm.

The

System can be programmed

generate

an alarm

after

aspecified

number

(one

six) ofconsecutive self-test

failures. (For most applications,

two

failures is an ade-

quate number.)

program

the

number

ofconsecutive

self-testfailures required beforean alarm is generated,

proceed as follows:

Reset the

6954

module as described in paragraph

4.038.

8. While holding

the

hold

pushbutton depressed,

momentarilydepress

the

advance pushbutton four

times.Then release theH

hold

pushbutton.Athree-

digit

number

with

the

leftmostpositionshould

appear in the channel display. The 4

denotes

the

fourth System operating parameter.

Depress theadvance pushbutton until the desired

number of consecutive self-test failures before an

alarm appears in the rightmost

digit

the

channel

display. Holdingtheadvance pushbutton depressed

causes

the

displayed number

be incremented

approximately 4times

per

second.

Reset the

6954

module as described

paragraph

4.038.

4.08

Programming

Multiple

System

Operating

Parameters.

In each of

the

preceding procedures for

programming System operating parameters, it is as-

sumed

that

only one parameter is being programmed.

If more than one parameter is being programmed, it is

not necessary

reset the

6954

module (as described

paragraph 4.038)

after

each parameter is pro-

grammed. After programming

one

parameter, hold the

hold

pushbutton depressed and momentarilydepress

the advance pushbutton until the leftmost digit of

the

channel display advances

the

number

correspond-

ing to the next parameter

be programmed. Then re-

lease

the

hold

pushbutton. After all desired para-

metershave been programmed, reset the

6954

module

as described in paragraph 4.038.

page

table

Data-transfer-rate

programming

for

remote

control/status

interface

port

data·transfer rate

6954

channel

(bits

per

second)

display

indication

300

103

600

106

1200 112

2400 124

4800 148

9600 196

4.05

Display

Timeout.

The

6954

module can be

configured

that

its LED's turn off approximately 1

minute

after

the

last control pushbutton

depressed.

enable

disable this feature, proceed as follows:

Reset

the

6954

module as described

paragraph

4.03.

8. While holding

the

hold

pushbutton depressed,

momentarilydepresstheadvance pushbuttontwice.

Then release

the

hold

pushbutton. Athree-digit

number

with a 2

the leftmost position should

appear

the

channel display. The 2

denotes

the

second

System operating parameter.

the

channel display

contents

are 201, display

timeout is enabled; if the channel display contents

are 202, display timeout is disabled. Depress the

advance pushbutton until the desired

contents

ap-

pearin thechannel display(each time theadvance

pushbutton

is depressed, the alternate

contents

appear).

Reset

the

6954

module as described in paragraph

4.038.

you momentarilydepressthe advance pushbutton

once. Repeat this until

the

channel display goes

blank. Resetting is

then

complete.

4.04

Data-Transfer

Rate

for

Remote

Cantrall

Status

Interface

Port.

To program

the

data-transfer

rate

for

the

RS-232-C remote

control/status

interface

port,

proceed

as follows:

Reset the

6954

module as described in paragraph

4.03.

8. While holding

the

hold

pushbutton

depressed,

momentarilydepresstheadvance pushbutton once.

Then release

the

hold

pushbutton. Athree-digit

number

with

a 1 in

the

leftmost position should

appear

the

channel display. The 1

denotes

the

first System operating parameter.

Determine

the desired data-transfer rate

for

the

remote

control/status

interface

port. Then refer

table

determine

the

corresponding channel

display contents.

If the

channel

display

contents

corresponding

the desired rate (in bps) are already present

the

channel

display, proceed directly

step

Other-

wise, depress

the

advance

pushbutton

advance

the

next rate. Repeat this until

the

desiredchan-

nel

display

contents

appear.

Reset the

6954

module

as described in paragraph

4.038.

practice

section

81251

channel

operating

parameters

4.09 The following operating parameters can be pro-

grammed individually

for

each channel via

the

6954

module'sfront panel: (1) bypass, (2)

off

hook, (3) cancel-

ler

only, (4) Hreset, and (5) Hhold. Refer to paragraph

2.07

for

descriptions of these parameters. Associated

with each

the

channel operating parametersis

acon-

trol

pushbutton

used

enable

disable

the

para-

meter

and a

control

LED

that

indicatesthe status ofthe

parameter.

4.10

additiontothecontrol

LED's,

twostatus

LED's

are provided on

the

6954

module's front panel. The

status

test fail LED lightswhenachannel failsself-test-

ing; refer

section9of

this

Practice

fordetails

on inter-

preting

the

status

this LED and the

channel

display.

The

status

bypass LED lightswhen

the

channel whose

number

isdisplayedin

the

channel

displayiseffectively

bypassed. It is important

recognize the difference

between

the

control

bypass and

status

bypass LED's.

The

control

bypass LED lights only when achannel is

bypassed

selecting

the

corresponding

control

by-

pass parameter. The

status

bypass LED lights when a

channel is effectively bypassed. Achannel is effectively

bypassed

under

any of the following conditions:

The channel is on-hook.

The channel'scontrolbypass parameterisselected.

The channel's Hreset parameter is selected.

The channel is bypassed upon receipt of data-dis-

abie tone.

4.11

examine

orto

program channel parameters,

proceed as follows:

Reset the

6954

module as described in paragraph

4.03.

Depress

the

advance pushbutton until

the

desired

channel number appears in

the

channel

display.

Holding theadvance pushbutton depressed causes

the

displayed

number

be incremented approxi-

mately4times

per

second. Ifthe programming is

be performedsimultaneouslyon all channels, select

channel numberOO.

Afterthe

desiredchannel num-

ber

is displayed in the

channel

display,

the

control

and

status

LED's indicate

the

existing program-

ming and status

for

the channel. Alighted

control

LED indicates

that

the

corresponding parameteris

selected.

select aparameter, depress

the

corresponding

control

pushbutton once.

cancel aselectedpara-

meter, depress the pushbutton a

second

time.

Repeat steps

Band

for

any

other

channels

programmed.

Reset

the

6954

moduleas described in paragraph

4.03A.

remote

system

control

5.01 The

251

System can, if desired, be controlled

from aremote iocation via aremote

controllstatus

interface

that

uses aserial data format compatible

with EIA standard RS-232-C. All channel-related con-

trol

functions

and status indications available via the

6954

Control Interface Module's front-panel pushbut-

tons

and

LED's are also available via the remote

controllstatus

interface. This section describes the

protocol

for

remote system control. Refer

para-

graphs 2.11 through 2.13

for

typical remote interface

configurations.

remote

interface

protocol

5.02

Serial

Link

Protocot

The

remote

interface

serial link is an RS-232-C full-duplex

asynchronous

link

that

uses seven-bit ASCII characters with

one

start bit,

one

stop

bit, and

one

even-parity bit. Serial

link

speed

can be 300, 600, 1200,

2400,

4800,

9600bps; the selected speed must be programmed

into

the

6954

module (see paragraph 4.04). The 251

System

echoes

all characters received; therefore,

the

controlling terminal

computer should be configured

for remote echoplex operation.

5.03

Command

Protocol.

All remote-control com-

mands consist of a

sequence

four

ASCII charac-

ters. The first character

sent

the

ASCII-encoded

System unit number of

the

System

be controlled.

Table 7lists

the

ASCII characters corresponding

each System unit number. System unit numbers are

assigned via the

6954

module's front-panel

controls

(see paragraph 4.06). For example, if System unit

211l

the

target

of aremote-control command,

the

first character of

the

four-character

sequence

would

be a

The

second

and

third

characters

sent

are

the

channel number of the channel

be controlled. For

example, if channel 7is

be controlled,

the

second

character of

the

four-character

sequence

would be

and the third character

would

The

fourth

char-

acter

sent

the

command key; command keys are

listed in

table

8and described

further

in paragraphs

5.05

through

5.11.

System System

unit number

ASCII

hex

unit

number

ASCII

hex

2b62 18 r72

3c63

573

211

t74

6f66

w77

8h68

x78

9i69 25 y79

26 z

k68

311

DEL

32 \

611

table

System unit number codes

5.04 Remote commands are

two

types: control

commands and status-request commands. Control

commands cause reconfiguration of the specified

channel. Status-request commands simply monitor the

existing configuration. When acontrol command is

sent, the targeted

251

System returns an

ACK

charac-

ter

(1Il6

hexadecimal) if

the

command is legal

NAK

character (15 hex) if the command is illegal.

Neither

ACK

nor

NAK

is returned in response

status

commands; only the status information is returned.

page 20

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