Digital Equipment DECTAPE DUAL TRANSPORT 555 User manual

H-555
DECTAPE
DUAL TRANSPORT
DIGITAL EQUIPMENT CORPORATIC.N • MAYNARD, MASSACHUSETTS

H-555
555
DEc-rAPE
DUAL TR}~NSPORT
DIGITAL. EQUIPMENT CORPORATIO'N • MAYNARD, MASSACHUSETTS

ICOpy NO.
This manual contains proprietary information. It is provided to the
customers of Dig ita I Equ ipment Corporation to he Ip them properly
use and maintain DEC equipment. Reveal ing the contents to any
person or organ ization for any other purpose is proh ibited.
Copyright 1965 by Digital Equipment Corporation
ii

Chapter
2
3
4
Appendix
'CONTENTS
INTRODUCTION AND DESCRIPTION •••
........................
Introduction •••••••••••••••.••.••
Specifications for DECtape Transport Model 555.
General .•••••.•••••
.................................
Tape Characteristics ••••••••••••••••••••••••••••••••••
Drive Characteristi cs •••••••••••••••••••••••••••••••
Control Inputs {ground leveI for assertion from -15 vdc}
Timing Consideration
•••••.••••.•••••••••••••••••••••••••••
Information Handling •.••••••.••••••••••••.••••••••••••••••
THEORY OF OPERATION .....................................
Drive Meehan ism ••• 0 •••••••••
.............................
Motion Control Relay Network ••
Automatic Operation •••••••
...........................
...........................
Manual Operation ••••••••••• 0 •• 0 •••••••••••••••••••••
OPERATION.
Controls
Manual Controls.
Tape Loading •••
MAINTENANCE
Adiustments ....... " ...................................... .
Cleaning ....•.....•.••..•..•.......•..•••....••..••.•••.
Connectors •• 0 •••••••••••••••••••••••••••••••••••••••••••
ENGI NEE RING D RA WING • ••• •. •• ••• ••••• •• ••• •• •• ••• •• • •• •• •
iii
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Figure
1
2
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4
ILLUSTRATIONS
Dual Transport Type 555 as shown in System I •••••••••••••••••••••
555 Timing Diagram .......................................... .
Dual Transport -Type 555 ••••••••.••.••••.••.•••••••••••••••••
Tape on Head and Guide ...•••.••.••••••.••••.••••••••••••••••
iv
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3-1
3-2

CHAPrER 1
INTRODUCTION AND DESCRIPTION
INTRODUCTION
The DECtape Dual Transport Type 555 is composed of the motor drives, tape heads, and control
relays necessary for the selection, motion control, and transfer of stored digital information.
The Type 555 records bits in the Manchester system (phase recording) at a density of 375 (plus
or minus 60) bits per track inch.
The dual transport consists of two logically independent tape transports each capable of han-
dling two 3-1/2 inch reels of 3/4 inch tape. The Mylar tape is 1.0 mil thick, 260 feet long,
and stores approximately 3 million bits. The transports are capable of bidirectional operation;
reading, writing, or searching can be done in either direction.
Rei iable recording is obtained by redundantly pairing the ten tracks of the head assembly.
The resulting tape recording consists of three paired information tracks, a pair of mark tracks,
and a pair of timing tracks. Since tape speed is approximately 80 inches-per-second, an
effective information transfer rate of 90,000 bits is achieved. No ~air of tracks is adjacent,
and redundancy is achieved by series wiring the two heads for a pair of tracks. On reading,
the analog sum of the heads is used to detect the correct value of the bits. Thus, a bit cannot
be misread unless the noise on the tape is sufficient to change the polarity of the sum of the
signals being read. Noise that reduces the sig1nal amplitude has no effect on bit detection.
The Type 555 Transport uses a simple drive system without capstans, pinch rollers, or tensioning
mechanisms.
The reels are designed so that the ratio of the outside tape diameter to the inside tape diameter
is a relatively low 1.3 to 1. Thus, the torque requirements and the tape tension are almost
constant in either direction throughout the tapE3 length.
1-,1

Figure 1 Dual Transport Type 555 as shown in System I
1-2

SPECIFICATIONS FOR DECTAPE TRANSPORT MODEL 555
Overall Size
Weight
Mounti"g
Power Requirements
Connectors
Cool ing
Operating Temperature
Humidity
General
10-1/2 in. high, 19-1/2 in. wide, 17 in. deep
651bs
Standard 19 in. rack. Four No. 10-32 screws spaced the same as
for a
standard 10- 1/2 in. pane I are used for mounting. Transport
extends 13 in. behind mounting surface. Desk model also available
on request (30 ft max interconnecting cable).
-15 vdc
115 vac ±1 00/0
2.0 amp max
1.2 amp idle
3.2 amp max
60-cycle mode Is standard, 50-cycle mode Is on request.
1 ea chassis-mounted male power socket
4 ea Type 133 male .22-pin amphenol connectors, paired to provide
jumpering to sequential transports for both head connection and
control connection.
Internally mounted f(lns are provided
50° F to 110° F ambient
10- 90% re lative hUIll id ity
NOTE: The manufacturer of the magnetic tape for DECtape
recommends 40-60% relative humidity and 60- 80°F as accept-
able for operating environment.
Capacity
Reel Size
Real Diameter
Tape Handling
Speed
Tape Charclcteristi cs
260 ft of 3/4 in. 1 mil Mylar sandwich tape
3-1/2 inches diameter
1 .3
Direct drive hubs and specially designed guides which float the
tape on a cushion of air. No capstans or pinch rollers are used.
90 ±14 ips
1-·3

Density
Information Capacity
Tape Motion
350 ± 55 bits per inch
2.6 x 106 bits per ree I assembled into computer length words by
control
Bid irectiona I
Drive Characteristics
Times given are for 90 percent full speed.
Start Time
<300 rns
Stop Time <150
rns
Turn Around Time <
300 rns
Start Distance
<9 in.
Stop Distance
9 ±2 in.
Control Inputs {ground leve I for assertion from -15 v dc}
8 selection lines
forward command
reverse command
GO command
STOP command
two
wire interlock for write ampl ifiers
1 ALL STOP line - absence of the ground level causes the unselected transpor~ to stop. Used
to stop transports when program stops.
All control inputs except the ALL STOP line require 150 rna dc max. The ALL STOP line re-
quires 1.2-amp dc max. (150 rna dc each drive).
TIMING CONSIDERATION
The 555 Transport uses relays wh'ich have a maximum operate time of 17 milliseconds. There-
fore, to insure reliable operation the commands to the transport must be held long enough for
the re lays to respond. See Figure 2 for acceptable command sequences and times.
1-4

Figure 2 555 Timing Diagram
NOTE:
1. Circled numbers indicate the minimum time in milliseconds
necessary for the transport to accept and hold the indicated commands.
2. Diamond shaped arrows indicate reversable paths.
3. Only those paths which are not illegal, meaningless or impossible
are shown.
4. A STOP command should not be given for at least 150 milliseconds
after a GO command.
INFORMATION HANDLING
Connection to the bus is done when a drive is se lected. The tape head is a lO-track head
paired to form five redundant channels; one timing channel, one mark channel, and three
information channels.
Information to and from each drive is accompl ished via the tape head which is connected to a
20-w ire bus.
'1·-5

CHAPTER 2
THEORY OF OPERATION
This section provides a functional description of the chassis wiring shown on Drawing No.
D-25326 in Appendix 1. The Type 555 is composed of two identical tape drives; only one will
be described here. The Type 555 can be divid.ed into three areas for the purpose of descrip-
tion: the tape head (see Chapter 1); the motors and their voltage supply network; and the mo-
tion control relay network.
DRIVE MECHANISM
Motor voltage is applied whenever the OFF-WRITE LOCK-WRITE switch is in either the WRITE
LOCK or the WRITE position. The motors are electrically connected for contrarotation and
are matched for equal torque characteristics at assembly. At standstill, equal voltage is appl ied
to both motors; the equal torques deve loped by the motors buck out any tape movement. The
tape moves when on~ of the 200-ohm resistors is shunted out in each motor voltage supply path.
The resulting increased current then allows that motor to develop more torque than its mate
and rotates the tape in the desired direction.
Braking occurs when tile 200-ohm resistor is momentarily shunted out in the voltage supply path
of the trai Iing motor wh i Ie inserting a 200-ohm resistor in the path of the leading motor. The
trailing motor then develops the greater torque until the tape is brought to a halt. At tape
halt, the 200-ohm resistor is reinserted in the voltage supply path of the trailing motor, and
equal voltages are again applied to both motors. Adjustments are provided to exactly govern
the duration in which braking voltage is applie~d to the trailing motor. A lOO-ohm resistor is
in series with the motor voltage supply paths to I imit power dissipation while the transport is
idle.
MOTION CONTROL RELAY NETWORK
The motion control relay network is composed of seven relays and a 3-position switch. The
network provides for tape motion under direction of an external control or under the direction
2-·1

of an operator. During automatic operation, the control appl ies ground-level reverse, forward,
stop, and go commands to the transport. The relay energizing voltage is taken from a -15 vdc
supply common to all relays. Each command line draws 120 rna de. The transport must first be
selected for operation before command signals can be appl ied; energizing the select relays
enables the command lines. The motion control commands are then appl ied to corresponding
relays that control the amount of resistance in the motor voltage supply paths.
In manual operation, motion is stopped in the AUTO position of the REV-AUTO-FWD switch.
Holding the switch in the REV or FWD position applies a ground to the appropriate relays to
command
motion to start in either the forward or reverse directIOn. Releasing the switch de-
energizes the relays and stops the motors.
Rei iable electrical operation is enhanced by the incorporation of damping networks and I imit-
ing diodes across the relay coils as well as arc-suppression networks across the relay and switch
contacts.
Automati c Operation
For automatic operation, the SEL.ECT switch must be set to the proper address, the OFF-WRITE
LOCK-WRITE
switch must be in either the WRITE LOCK or the WRITE position, and the REV-
AUTO-FWD switch must be in the AUTO position. The red lamp is illuminated when
a switch in the control is set to write "mark and timing" information on the tape. This lamp
warns the operator that the write ampl ifiers for the mark and timing track are enabled and if
any write commands are given, the mark and timing channels will be destroyed. When the
OFF-WRITE LOCK-WRITE switch is not in the OFF position, operating power is appl ied to the
motors. However, the motors are held at standstill by the equal voltages developed across the
series-parallel resistor network. Thus, the unit is ready to operate under command of the ex-
terna I control, but command signa Is cannot be appl ied until the transport is se lected for operation.
The transport is selected by a select command {ground} appl ied through the SELECT switch.
The select command energizes the SEL 1 relay K3. When K3 is energized, it enables the FWD
and REV command lines; it also energizes the SEL 2 relay K5 through contacts 1 and 3 of K3.
The energizing of K5 enables the STOP and GO command Iines and also appl ies energizing
voltage to the head relays. Thus, once a select command is received, the motion control
2-2

command paths are enabled and the head relays; are energized. In addition, the write inter-
lock loop is completed through contacts 1 and :3 of K5. The transport is now ready to rece ive
motion commands.
Motion Commands
Assume that the transport rece ives a FWD command (ground). The command energizes the FWD
relay K4 and connects it to a latching network through its normally open contacts 6 and 7 and
the normally closed contacts 1 and 4 of REV rel:ay K7.
Now, assume that a GO command (ground) is Clppl ied to the transport. The command energizes
the GO relay K2 and connects it to a latching network through its normally open contacts 1
and 3 and the normally closed contacts 1 and 4 of STOP relay K6. Closing the GO relay K2
places ground on the TIME re lay K1 through contacts 6 and 7 of K2. The TIME re lay K1 ener-
gizes, and the RC time constant across its coil begins to charge. The charging time is adjusted
by the 1K variable resistor (R2 or R4).
When the TIME relay K1 energizes, the tape begins to move forward. initially, the motors
are held ot standstill by the equal voltages developed across the series-parallel resistor net-
work. When the TIME relay Kl energizes, the~ 100-ohm resistor in the motor voltage supply
,
path is shunted out by a 2-ohm resistor. When the TIME relay K1 energizes, operating vol tage
for the FWD motor is devf' loped through the parallel combination of the 2-ohm resistor and the
100-ohm resistor; the vol tage is appl ied through the closed contacts 1 and 3 and 11 and 9 of the
TIME relay Kl. With nearly full line voltage applied, the FWD motor produces greater torque
than the REV motor and moves the tape forward.
Stop Command
Assume that a STOP command is now appl ied to the transport. The command (ground) energizes
the STOP relay K6, interrupting the latching circuit at its contacts 1 and 4 for the GO relay.
The GO relay K2 immedia·tely de-energizes. However, the TIME relay Kl is held energized
by the RC network across its coil for a period dependent on the charge of the capacitor. Since
one leg of the RC network Iimits the charging time of the capacitor, the amount of charge (and
2--3

the time to discharge} is a function of the time the transport has been in motion. During the
period when the GO relay K2 is de-energized and the TIME relay Kl remains energized, the
vc)ltage formerly used to drive the FWD motor is appl ied through the normally closed contacts
11 and 8 of the GO relay K2 as braking voltage for the REV motor. When the TIME relay K1
de-energ izes, the motors stop. The motors are then he Id at standsti II by the equa I vol tages
deve loped across the 200-ohm resistors and the 100 ohm-I im iting resistor. The transport has
been designed to retain all motion commands. Therefore, if selection to the transport is re-
moved, the last motion command will dictate its condition.
RE3verse Command
A
REV command (ground) energizes the REV relay K7, opening its normally closed contacts 1
and 4 to unlatch the FWD relay K4. Note that the FWD relay K4 latches on the receipt of
the first FWD command and remains latched until a reverse command is received.
Operation for a reverse command is identical to that for a forward command, with the obvious
exception that resistance is shunted out of the REV motor vol tage supply path to move the tape
in the reverse direction.
Manual Operation
In manual operation, the OFF-WRITE LOCK-WRITE switch must be either in the WRITE LOCK
or the WRITE position. During manual operation, the write interlock loop is interrupted and
the transport cannot respond to write commands from the control.
TClpe movement during manual operation is manipulated by the REV-AUTO-FWD switch. Assume
that the switch is held in the FWD position. Ground is applied from pin D of P4 through con-
tacts 1 and 2 of the D section of the REV-AUTO-FWD switch to energize the FWD relay K4.
Simultaneously, ground is applied through contacts 1 and 2 of Section C of the switch to en-
ergize the GO relay K2 and the STOP relay K6. The 50 MFD capacitor on the line to the
STOP relay K6 charges to the relay energizing voltage. When the GO relay K2 is energized,
it immediately energizes the TIME relay Kl. Resistance is then shunted out of the FWD motor
vol tage supply path and the tape moves forward.
2-4

Returning the REV-AUra-FWD switch to the AUra position removes the ground from the GO
relay K2 and it immediately de-energizes. The motors are then braked to a holt in the usual
manner. The charge on the capacitor holds the STOP relay K6 energized for a short period
after the GO relay K2 de-energizes; this guarcmtees that the transport to come to a halt. The
sequence of operations to stop the drive is the same as described for the stop command (pre-
viously explained under Automatic Operation) ..
Placing the REV-AUra-FWD switch in the REV position has the same effect, except that REV
relay K7 is energized, opening its normally closed contacts to allow the FWD relay K4 to
de-energize to insure reverse motor rotation.
2--5

CONT/(OLS
-----..:..:--
The DECtape Dual TransPOrt Type 555 is fitted With duplicate COntrols for each channel (Figure 3).
Figure 3 Dua I Transport _ Type 555
~.2NTR~
OFF - WRITE LOCK - WRITE _ SWitch
In the OFF Position the AC voltage to the motors is interrupted. The WRITE Position completes
the 2-wire interlock
if the drive is selected. The WRITE LOCK Position supplies 117 vac to
the motors and inhibits write functions via the 2-wire interlock.
3-1

REV -AUTO - FWD. -Switch
Provides manuaI control to move tape either reverse or forward. The AUTO position returns
motion control to
the DECtape control.
Selection Switch
Allows the user to designate any available drive to the number desired. Numbers provided are
1-8, inclusive.
~Indicator Lamp
A red indicator lamp warns the user that the writers for the timing and mark track are enabled.
TAPE LOADING
The 3-1/2 inch tape reels are loaded by pressing the reel onto the hub, bringing the loose end
()f the tape across the tape head, and attaching it to the take-up reel. The reels are then spun
by hand for a few
revolutions. The AUTO-REV-FWD control allows the user to manipulate the
i"ope in either direction. Figure 4 shows the tape properly loaded on the tape head and tape
~~u ide.
Figure 4 Tape on Head and Guide
3-2

CHAPTER 4
MAINTEINANCE
ADJUSTMENTS
There
is only one type of field adjustment on the 555: the "STOP" time adjustment on the rear
of the chassis governs the time interval in which the time relay remains energized. The adjust,-
ments are shown below.
CHASSIS REAR VIEW 8
Rl
§
R2
@
R3
§
R4
Rl - Side B Long "Gall Time "Stop" Adjustment
R2 - Side B Short "GO" Time "Stop" Adjustment
R3 - Side A Long "GO" Time "Stop" Adjustment
R4 -S ide A Short "GO" Time "Stop" Adjustment
NOTE: Clockwise adjus·tment decreases resistance.
There are two "STOP" adjustments for each drive, a long "GO" time "STOP" adjustment and
a short "GO" time "STOP" adjustment. The long "GO" time "STOP" adjustment (LGSA) is
used to correct the stop characteristics of a drive which has been running at full speed. There-
fore, when ad justing the LGSA, the drive mus1- be in motion for longer than 1 second. The
short "GO" time "STOP" adjustment (SGSA) is used to correct the stop characteristics of a
drive which has not attained full speed. The SGSA is done for a GO command of 120 milli-
seconds.
4-1