Digital Equipment TU55 User manual

H-TU55
~--. -
INSTRUCTION MANUAL
DECTAPE TRANSPORT
" -.... -_.
DIGITAL EQUIPMENT CORPORATION • MAYNARD, MASs4cHUS~TTS
"'¢ ,,'" ..

DECTAPE TRANSPORT
TU55
INSTRUCTION MANUAL
H-TU55
DIGITAL EQUIPMENT CORPORATION • MAYNARD, MASSACHUSETTS

This manual contains proprietary information. It is provided to the
customers of Digital Equipment Corporation to help them properly
use and maintain DEC equipment. Reveal ing the contents to any
person or organization for any other purpose is prohibited.
Copyright 1966 by Digital Equipment Corpora:tion
ii

1.1
1.2
1.3
1 .3.1
1 .3.2
1 .3.3
1.4
loS
1.S.1
1.6
2
2. 1
2.2
2.2.1
2.2.2
2.2.3
2.2.4
2.2.S
2.2.6
2.2.7
2.2.8
2.2.9
2.2.10
2.2.11
2.3
2.3.1
2.3.2
2.3.3
DECTAPE TRANSPORT TUSS
CO NTE NTS
INTRODUCTION AND DESCRIPTION ...........•..•..........•.........
General Description ..•.••.•.•••..••..•....••••.••.•.••....••.•••..
Scope of Manua I .••••..••••.•.•••••••••.•••.•....••....•...•..•.••
Pertinent Documents ......•..................•.•......•.•.•...••...
Manuals ..........•...................•.•.•.....•...•..••.•..
Engineering Drawings .........••..........•..•........•.......•
New Module News Bulletins ...................••...•.•.....•...
Functional Description .....•.•...•.••..•.•..•..•...•.•..•..•...•...
Phys ica I Descri ption .......•............•...•..•.....•..•••.•.•....
Electrical Details ............••.••.•.............•....•.••....
TUSS Performance Characteristics ....••..•..........•.....•.....••...
THEORY OF OPERATION .......•..................•...........•.......
Block Diagram Analysis •.•..............•.....•..•••..•.•.•..•..•..
Detailed Descriptions .....•••..•.........•..•.••..•.••............•
Interface .............. : ........•..•............•.....•.......
Unit Select Lines ...........•....•....•.........•........•.••.•
Command Lines ..•..•....•.....•..•..•........ ~ .......•..•....
WRITE ENABLE Signal
Interface Connections
Read/Write Head ..................•........••...•.••.....•••..
Tape Motion Control ..........••.•..•.•........••.•..•••..•..•.
Remote or" Programmed Control •..•..••.••••.••.•...•.•...•.••••.
Local (Manual) Control ....•.........•.•.•..•.•••...••.•....••.
Motor Control ......•.....•........•..••........••..•.....••..
Transport Selected Signal .............••..•............•....••.•
Module Descriptions ..........................•.•........•.•.......
Type R303 Integrating One Shot (Delay) .......•....•..•..........
Type WS13 Level Amplifier ..................•.......•..........
Type G8S0 SCR Motor Driver ..................•........•.......
iii
Page
1-1
1-1
1-2
1-2
1-2
1-2
1-3
1-3
1-4
1-6
1-9
2-1
2-1
2-4
2-4
2-S
2-S
2-S
2-6
2-6
2-6
2-6
2-7
2-7
2-8
2-9
2-9
2-10
2-10

3
3. 1
3.2
3.2.1
3.3
4
4. 1
4.2
4.2.1
4.2.2
4.3
4.4
4.5
4.6
4.7
4.8
5
5. 1
5.2
5.3
5.3.1
5.3.2
5.4
Figure
1-1
1-2
1-3
1-4
1-5
DECTAPE TRANSPORT TU55
CON TEN TS (Continued)
OPERATION .•••.•..••..•••••...•.•••.•.••••.••.•..•... ' ..•..•........
Introduction ....•.•...•...••.•....................•. ' ..........•...
Controls and Indicators ...•..........•....••......•........•........
Operating Notes ....•.•....•..••.•.•....•..••...•..•••..•.....
Loading Tape ........•.......••.•.•.•........•.•..•.......•..•...•
MAINTENANCE •..•....•..•.........••...••.............•.•......••..
Equipment Required •.•.•..••...•..•..••••.•..•...•.•.• ',' ••..••••..•
Preventive Maintenance •••••••.•.••..•..•.•.•......•..•..•.•..•....
Weekly Schedule ...•.•...•••......•.....•.•...••..•..•.•...•..
Monthly Schedule ..•.••.••••.••.•..••...••...•................
Tape Tension and Transport Stop Ad justment .•••.•.•.•.•.•.•.•..•..•.•.
Head Output Check ..•..•••••.••.•...•.••..•.••••.••.•..••.••••.•.
Head-Skew Check ..•.•••..••••.••••....•.••..•.••••••••.•.•.•..••.
WRITE ENABLE Circuit Check .••••••..•.••..••.•.••.••...••.••••..••
Troubl eshooti ng ••.••.•..•••••••.•...•.••.•...•.••••...•...•.•..•..
Recommended Spares ..•.••••••••••.•..•.•••••••••.•.•.•..•••..•••••
ENGINEERING DRAWINGS ••.•••••.••••••.•..••••..•.••••.••••..•••••.
Introduction .•••••••••••••••••••.•••..••••••••.••.•.••...••••••.••
Circuit Symbols ......•.•........•.•......•....••..•.•.••..••••.•••
Logic Signal Symbols ..•.•.••.••.••.•..••.•••.•.•..•....•........•.
Logic Levels .•..•..•..•.•..••••.•....•••....•......•..••......
FLIP CH IP Pulses .•..••••••..•••..••••••••.•••••••.•....•••....
Semiconductor Substitution .........................................
ILLUSTRATIONS
Type TU55 DECtape Transport ••.•.•.••••..•...•••.•..••...•.••..•..•.•..
Hub and Reel Assembly ......................•..........................
Arrangement of DEC tape Head .••••.••...•••....•...•....•.•.••..••.....
Type TU55 DECtape TransportI Rear View .•••••..•.•••.•••...•.......•.••.
TU55 Interface Connections .•....•••.•••••.•••..••.••••.•••••••.•.•.••••
iv
Page
3-1
3-1
3-1
3-1
3-1
4-1
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4-1
4-2
4-2
4-3
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4-5
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4-7
5-1
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5-4
1- 1
1-5
1-6
1-7
1-8

2-1
2-2
2-3
4-1
5-1
5-2
5-3
Table
1-1
2-1
3-1
4-1
4-2
5-1
Drawing
DECTAPE TRANSPORT TU55
CON TEN TS (Continued)
DECrape Transport TU55 Block Diagram
•.••.•••••••.••••.••••••••.••.•.•••
Head Connections •••••••.•.•.•••••••••••.••••.••••••.•••••••.•••.•••.•
Symbol ized Schematic of G850 SCR Motor Driver •••••••••••••••••••••••.••
Modu Ie Ad justment Tri mpots .•••••••••..••..•..•..••••••••....••.•...•..
DEC Symbols ...•..........••..•....•....•.•..••.••....•.•....•.......
FLIP CH IP R-Series Pulse .•.•.....•.••.•••..•....•.........•.•....•.....
FLIP CHIP B-Series Pulse •.....•.....•....•.••.•.•.•.•........••.•..•.•.
TABLES
Summary of Equipment Characteristics for the TU55 DECtape Transport ..••....
Motor and Brake Operation Truth Table ..•...••.....•........•.••.•.•..•..
Functions of Controls and Indicators .•.•••••.•...•..•........•.•......••.•
Recommended Maintenance Equipment .....•.••.......•..•..•.............
Recommended Spare Parts •••••.•••••••••••••••••.•.•..•.••.••.•.•••..••
Semiconductor Substitution ••••.••••••••••••••••••.•••••••.••••.•.••••••
ENGINEERING DRAWINGS
BS-D- TU55-0-2
MU- D- TU55-0-5
WD-D- TU55-0-4
WL-A- TU55-0-3
CP-A- TU55-0-6
RS-B-G850
RS-B-G851
RS-B-R002
RS-B-R107
RS-B-Rll1
RS-B-R202
So Iid State DECtape Transport ••••••••.•••.••••.••••••••.•.••
Module Utilization List •••••.••••.••••••••.••.••...•..•....•
Bus Bar for TU55 •••••••.••••••.••.••••.••••.••••.••...•••••
TU55 Transport Wiring List ••••••••••••••••••••••••..•••••.•••
Components List •••.•••••••••••.••••••••••••••••.....•.••••
SCR Motor Driver ••..•••.••.••••••••••••••.••••.•••••••••••
Re Iay ••••.•••••••.•••••..•••.••••••.•••••••••••..••..••••
Diode Cluster ••••••••••••••.•••••••••••••••••••••••••••.•••
Inverter ••••••••••.•••••••.••••.•••••••..•••.••••.••...•••
Diode Gate •••..••••••••.••••.••.•.•••••••.••••.•••..•••••
Dual FI ip-Flop •••••.•••.•••.••..•••..•••..••••.••••.•.••.••
v
2-1
2-4
2-11
4-3
5-2
5-4
5-4
1-9
2-9
3-2
4-1
4-7
5-4
5-5
5-7
5-9
5-11
5-12
5-13
5-13
5-14
5-14
5-15
5-15

Drawing
RS-B-R303
RS-B-W023
RS-B-W032
RS-B-W040
DEer APE TRANSPORT TU55
CO t\l TEN TS (Continued)
Page
Integrating One-Shot •.....•..•.••.....•....................•...• 5-16
Ind icator Ampl ifiers
5-16
DECtape Signal Connector •••....•...•..••••...•.........•...•.. 5-17
Solenoid Driver...... • . • • . . . . . . . . • • . . . • • . . . . • . . . • . . . . • . . • . . . . . • 5-17
VI

DECT APE TRANSPORT TU55
CHAPTER 1
INTRODUCTION AND DESCRIPTION
1.1 GENERAL DESCRIPTION
The Type TU55 DECtape Transport (see figure 1-1) is a sol id-state, bidirectional, magnetic-
tape handl ing device designed and manufactured by the Digital Equipment Corporation (DEC) for use in
DEC digital computer systems. When used witha suitable DECtape control system, the TU55 provides a
fixed-address magnetic-tope facility for high-speed loading, readout, and program updating. The DEC-
tape control system directs the transport to read forward or in reverse, to write forward or in reverse, to
stop, and to go. The TU55 contains tape handling elements, drive mechanisms, and solid-state switching
circuits which switch the tape head onto a master bus system and interpret command instructions from the
control un it. The highly rei iable sol id-state switching circuits in the TU55 are completely compatible
with the older Type 555 DECtape Transport (which uses relay switching) and may be used to modify and
expand systems employing the older type transport.
Figure 1-1 Type TU55 DECtape Transport
1-1

DECT APE TRANSPORT TU55
1.2 SCOPE OF MANUAL
This instruction manual is intended to aid personnel in the maintenance of the TU55 DECtape
Transport. The equipment is discussed primarily from a maintenance point of view, but some information
is given on the operation of its associated controls and indicators. Pertinent documents I isted in the fol-
lowing subsection contain more complete information on operation from a F>rogrammer's viewpoint.
Since the transport is one element of a computer/control/transport system, the reader is in-
vited to fam il iarize himself with the internal operations of both computer cmd control. Of spec ial
importance are the sections concerning program interrupts, programmed in/out transfers, and the data-
break facility in the computer; and the select and motion control logic in the external DECtape control.
Detailed descriptions of the tape format, instruction repertoire, and progn::lmming practice for using the
TU55 with a particular computer can be found in the user handbook for th~~ computer. Control informa-
tion for the TU55 can be obtained from the maintenance manual for the DECtape control system used
with the transport.
1 .3 PERTINENT DOCUMENTS
The following documents provide source information relative to the use of the DECtape Trans-
port Type TU55:
1 .3. 1
1 .3.2
Manuals
Digital FLIP CH IP Modu les Catalog, C-105
PDP-7 User Handbook, F-75
PDP-8 User Handbook, F-85
DECtape Control 550 Instruction Manual, H-550
DECtape Control 551 Instruct ion Manual, H-551
DECtape Control 552 Instruction Manual, H-552
DECtape Control TCOl Instruction Manual, H- TC01
DECtape PDP-8 Programming Manual, Digital-8-27-U
Engineering Drawings
A
set of reduced' engineering drawings for the TU55 is contained in chapter 5. These drawings
are in addition to the complete set of full-size drawings forwarded with eClch TU55. As explained in
chapter 5 all maintenance personnel should use only the full size engineering drawings for work on the
equ'ipment because these drawings show v(Jriations pecul iar to an individuol installation.
1-2

DECT APE TRAI'lSPORT TU55
1.3.3 New Module News Bulletins
G850 SCR Motor Driver
G8S1 Relay
W513 Level Ampl ifier
In addition to the above documents, complete sets of Library Programs are available for each
computer using DECtape systems.
1
.4 FUNCTIONAL DESCRIPTION
The TU55 Transport provides a read/write head for recording and playback of information on
five channels of the O.75-inch tape. Each channel consists of two nonadiace~t coils which are wired
in series. Thus, information on one track combines with redundant information on another to create a
single signal. Connections from the read/write head are made directly to the external control unit which
contains the read and write amplifiers as well as the command logic for the selection and remote control
of tape motion.
The left hal f of the front panel (see figure 1-1) contains the tape deck with reels and reel
motors, tape guides, and the read/write head; the right half is the local control panel with rocker
switches for selection and manual operation. The 600-rpm induction motors that drive the reel hubs
directly control tape motion. No capstans, pinch rollers, or drag pads contact the tape.
The logic circuits of the TU55 command tape movement in either direction over the read/write
heads. Soliq-state switching circuits completely control the tape drive motors. These circuits govern
the torque applied to each reel motor to transport the tape across the head in accordance with specific
commands (i .e., go, forward, reverse, stop).
In normal tape movement, full torque is appl ied to the take-up reel, thus establ ishing the
direction of motion. Reduced torque, applied to the trailing reel, maintains proper tape tension. Tape
motion is bidirectional so that either reel can serve as the take-up reel. The DECtape system uses the
so-called Manchester phase recording technique rather than an amplitude sensing technique; thus, tape
speed need not be a prec isely controlled parameter. Actua"y, the speed varies ±20%, depending upon
the diameter of the tape pack on the take-up reel. An electromagnetic brake mounted on each motor
shaft achieves a positive stop by braking the trailing reel at the end of a motion command. The take-up
reel motor continues to apply partial torque to take up tape slack. Whenever the tape is motionless,
one of the two reel brakes is appl ied opposite to the direction of the last tape movement.
1-3

DECT APE TRANSPORT TU55
Tape movement is controlled either by commands originating in the computer and applied to
the TU55 via a suitable DECtape control system, or by commands generated through manual operation
of rocker type switches located on the front panel of the transport. Typical DECtape control systems
which allow transfer of information between the computer and the TU55 are as follows:
Computer
Typical
DECtape Control System
PDP-1, -4 and -7
Type 550
PDP-6
Type 551
PDP-5 and -8
Type 552
PDP-8
TC01
PDP-9
TC02
Manual control is used to mount new reels of tape on the TU55 or as a quick maintenance check for
proper operation of the control logic in moving the tape.
External DECtape control systems may control up to eight individually addressed TU55s to
read or write tape. The operator may select the address of each drive by adjusting the thumbwheel
selector at the center of the TU55 local control panel (see figure 1-1). The operator may also place
the drive off-I ine by a setting on the same thumbwheel or by switching the drive for local operation.
In local operation, the head is disconnected and the rocker switches on the local control panel regu-
late tape motion.
1.5 PHYSICAL DESCRIPTION
All components of the TU55 are mounted on a preformed and assembled chassis. Roller slides
that allow easy access to the top, sides, and rear of the drive hold the chassis in a standard DEC bay.
Double doors in the front and rear are held closed by magnetic latches. Power supplies and controls
are mounted on the rear of the DEC bay. Generally, the transport is mounted with others in the same
bay that contains the DECtape control system.
The tape deck is machined from 3/8-inch cast aluminum plate cmd held to the chassis by cap
screws at the corners. Reel motors, tape guides and the head are secured only to the deck. This
arrangement preserves the integrity of the tape al ignment by the rigidity of the deck plate. Heavy
extruded aluminum plates at the top and bottom front of the chassis serve CIS bumpers to protect the
deck and control panel. The head is mounted in direct contact with the deck and is secured at both
sides by brackets. Head azimuth is set during manufacture of the drive and cannot be adjusted in the
field.
1-4

DECT APE TRANSPORT TU55
CAUTION
No attempt should be made to loosen the brackets and change the head
position. .
Reel motors
are held by four cap screws (hidden by the reel hubs) from the front of the deck.
At the rear of the shaft (which extends from both ends) is the electromagnetic brake. At the front, the
shaft has a flat for securing the reel hub by a single Allen-head set screw. The hubs are flanged at the
rear and have an annular spring resting in a slot cut into the reel circumference. Beneath the spring in
the slot is a rubber ring seal which causes the spring to protrude above the slot to secure the reel (see
figure 1-2). The reel is a 1-piece mold of phenol ic composition. The inside circumference at the back
of the reel fits the hub. In front, however, the inside circumference is slightly larger, allowing the
hub spring to expand outward and to secure the reel. The clearance between the rear of the reel hub
and the tape deck is nominally 15 mils, but may vary on individual machines to guarantee proper tape
alignment in the guides. The guides are machined from aluminum and have a curvature designed to
maintain air-film lubrication between the tape and guides as long as tape is in motion. A fan mounted
on the topchassis plate continuously blows cool ing air over the reel motors.
REEL
FLANGE
SPRING
MOTOR SHAFT
RING SE AL --rj---+-l--L_
REEL
SPRING
Figure 1-2 Hub and Reel Assembly
1-5

DECT APE TRANSPORT TU55
The
redundantly paired tracks that form the five channels on the head are illustrated sche-
matically in figure 1-3. Three track pairs are used for data; the remaining pairs are used as timing and
control information. The two timing tracks are on the outside at opposite slides of the tape. Just inside
these are the two tracks for the mark channel, the contents of which signify to the external control the
type of information in the data channels. The six tracks for these data channels are grouped at the
center, where they are least affected by skew. Since writing may take place in the data channels
. while reading takes place simultaneously in the timing and mark channels, the tracks for the latter
channels are separated sl ightly from the data channel tracks to allow room for additional shielding.
I
L___ "---_ ~~6iH ---------e.J
r--- 0.750" l
r-- SPACING ~
I .088" I
TAPE
DECK
PLATE
II AUGMENTED II
ST~~2~~g~1 t--l . H r--'i -II I
.073" I M ~ ~ ~ _ _ l M
I -t--r---- I
I OAr~T T I
I CHI~~ I
I
DATA I
CHAN
2'---+------..1
DATA
I CHA~ I
I MARK
C"ANNEL I
TIMING CHANNEL
Figure 1-3 Arrangement of DECtape Head
Electrical Details
The TU55 requires the DEC standard +10 and -15 vdc power levels at the terminal-tab con-
nectors on the rear panel (figure 1-4). These dc levels are normally provided from power supplies
assodated with the DECtape control system. Ac power (1 05-125v, 60 cps) is connected at the 3-
terminal receptacle on the rear panel.
1-6

DECTAPE TRANSPORT TU55
Figure
1-4 Type TU55 DECtape TransportI Rear- View
Signal connections to and from the DECtape control system are made through 18-pin and
36-pin FLIP CHIP cable terminators that plug directly into the module mounting panel on the rear
panel (figure 1-4). Cable locations in this mounting panel are shown in figure 1-5 with respect to the
other installed modules. The command cable terminator is a Type W023 18-Pin Connector for the logic
signals governing selection and tape motion. The head signal connector is a double-size Type W032
36-Bit Connector for shielded cable. Two sockets at the TU55 logic panel are reserved for the command
connector and two for the information connector. The pins for each pair are bussed together. This is
done so that TU55s may be grouped. Each TU55 receives its information and commands from one trans-
port in the group through one set of connectors and sends these to the next transport through another set
of connectors.
The writing current is 210 ma. Playback peak-to-peak channel voltage is between 10 and
12 mv when the tape is up to speed.
1-7

DECTAPE TRANSPORT TU55
...J
Wa::
20
<u-
a..U
W
1-2
22
00
a::U
LL
R
303
R
303
Figure 1-5 TU55 Interface Connections
2
o
fi
~
a:: a::
i2~
~U
~W
...J2
«2
t5
8
U;
o
«
W
J:
Command signal levels from the DECtape control to the TU55 Trc::msport are either ground or
-3v. (Equivalent signals to a 555 Transport are either -3 or -15v.) For existing systems with a con-
trol system for the 555 Transport, exchanging a single FLIP CHIP module (a W513 Level Amplifier when
the rU55 Transport is connected to a contr1ol designed to drive relay Transport 555; otherwise a W990
Blank Module) allows the TU55 to accept command signals of either type.
The reel brakes and the head relay are energized by -15v throu!~h spec ial solenoid driver
circuits; the motors are controlled by silicon controlled rectifier (SCR) circuits that phase-switch the
110 vac I ine power.
The TU55 uses twelve types of FLIP CH IP logic modules (connec1"ors excluded) as follows:
2
W040 Solenoid Driver 2 R202
Duall FI ip-Flop
W513 Level Ampl ifier
R303 Inte!~rating Delay
1 R 107 Inverter
2 G850 SCR Motor Driver
4 R111 Diode Gate
G851 RelclY Module
R303 Integrating One-Shot
3 W023 Indi'cator Ampl ifier
R002 Diode Network
W701 Input Network
All modules are mounted on a d'ip-soldered epoxy board with 18 gold-plated contacts at one
end (36 on double-height modules) for connection to the mounting panel receptacle, and a plastic handle
bearing the type number at the other end. Three contacts on each modu Ie are reserved for supply voltages:
A and B supply the + 10 and -15v standard power levels; C is the ground.
1-8

DECTAPE TRANSPORT TU55
1
.6 TU55 PERFORMANCE CHARACTERISTICS
A summary
of the characteristics of the TU55 equ ipment is given in table 1-1 •
TABLE 1-1 SUMMARY OF EQUIPMENT CHARACTERISTICS
FOR THE TU55 DECT APE TRANSPORT
Overall Size
Mounting
Power Requirements
Connectors
Cool ing
Operating Temperature
Humidity
General
10-1/2 in. high, 19-1/2 in. wide, 9-3/4 in. deep
Standard 19- in. rack. Four #10-32 screws mount chassis
track assembly which holds transport.
C"hassis can be extended 16-3/4 in. beyond mounting
surface for maintenance
-15vdc,l.0ampmaximum
+10 vdc, 50 ma maximum
115 vac ±10%, 1.0 amp idle, 2.0 amp maximum current
(60- and 50-cyc Ie models)
Commands: two 18-terminal FLIP CH IP female
connectors
Information: two 36-term inal FLIP CH IP female
connectors
Internally mounted fan
50 to 11 O°F ambient
10 to 90
%
relative humidity
NOTE: The manufacturer of the magnetic tape for DECtape recommends 40
to 60% relative humidity and 60 to 80°F as acceptable for operating environ-
ment.
Tape Characteristics
Capacity
260 ft of 3/4 in., 1 mil thick Mylar sandwich tape
Reel Diameter 2-3/4 in. empty reel, 3-3/4 in. for 260 ft of tape
Reel Diameter Ratio Approx •. 1:4 (maximum to minimum)
1-9

DECTAPE TRANSPORT TU55
TABLE 1-1 SUMMARY OF EQUIPMENT CHARACTERISTICS
FOR
THE TU55 DECTAPE TRANSPORT (continued)
Tape Handling
Speed
Density
Information Capacity
Tape Motion
Tape Characterist ics (conti nued)
Direct drive hubs and specially designed guides which
float the tape over the head hydrodynamically. No
capstans or pinch rollers are used.
93 ±12 ips
350 ±55 bits per inch
2.7 x 10
6
bits per reel assembled into computer-length
words by external DECtape control
Bidirectional
Drive Chara'cteristics
Times given are for 90% full speed.
Start Time
Stop Time
Turn Around Time
Commands*
Unit Select*
Control
<150 msec
<150 msec
<250 msec
Input Signcds
to Transport from Control
FORWARD}
REVERSE
GO }
STOP
ALL HALT
(
ground level Clssertion, '\
normally complementary levels)
(
ground level ,assertion, )
normally complementary levels
(
negative level assertion used to stoP'\
transport when computer halts )
SELECT 1 through SELECT 8 (the selected line will
be at ground)
Output Signal from Transport to Control
WR ITE ENABLE (standard DEC ground level assertion)
*Valid only when the control is operating the solid-state Transport TU55. \Nhen relay type transport
(Type 555) signals are received a conversion is made to DEC standard levels by the W513 Level
Amplifier which converts the -3v level to ground and the floating input to ,-3v.
1-10

DECT APE TRANSPORT TU55
CHAPTER 2
THEORY OF OPERATION
2.1 BLOCK DIAGRAM ANALYSIS
The TU55 logic is shown in the functional block diagram of figure 2-1. All front panel con-
trols and indicators are shown within the blocks representing the associated logic. The functions of these
controls and indicators are summarized in table 3-1. Diamonds indicate the direction of signal flow be-
tween blocks; an open diamond represents a signal effective (asserted) at ground; a closed diamond rep-
resents a signal asserted at -3v. All interface signals are received from or transmitted to an external
DECtape control system. One of the two connectors at .the left of figure 2-1 serves as a command and
information signal bus to other TU55s.
A5 A6
"
,.........
.-....
~
-
'---'
'--'
AB2 AB3
" "
-
~
~
--'---'
.-....
WRITE ENABLE
...,
I
WRITE
SELECT
ENABLED
SELECT
B
ADDRESS LOGIC
II
..-
(8) WRITE
DELAY (0)
JAND
1 RIGHT BRAKE
LOCK
~
1
~-
1
TDELAY(I) ~
1._
SELECT
~ANDI
LEFT BRAKE
1I DELAY
(1)
DELAY 0)
I
~-
lELECTED
.-
STOP TORQUE....
..- REMOTE
----.
MOTION (0)
~ANDl
"" GO
B
BoFf3
------
.....
~
-GO
~I OR I
FULL TORQUE.... RIGHT
..., DIRECTION (1 ) MOTOR
STOP
.-....
._FWD
~--.J
......
DRIVER
..., LOCAL
~ANDI
I DRAG
TORQUE..-
FORWARD~
.....
""
MOTION (I)
.-
REVERSE MOTION
~GO
DRAG TORQUE.-.
ALL HALT..-
CONTROL DIRECTION
(0)
~ AND REV
.....
.-
--
lOR l
FULL TORQUE ..-
LEFT
I • -
.....
MOTOR
I
~ANDI
--
STOP TORQUE.... DRIVER
r---
SELECTED
......
SKEW MEAS. (1)
-
TMG (4) _TMG (4)
MRK (4)
HEAD }t1RK
(4)
_DATA 1 (4)
RELAY
]lATA 1 (4)
HEAD
~
DATA 2 (4) ]lATA 2 (4)
,.DATA 3 (4)
yATA 3(4)
-
----
NOTE: An arrow signifies a nonstandard DEC signal, such as motor voltage,
head playback, brake voltage, etc.
In the motion control block the arrow above a switch means that pressing this
switch results in tape movement in the indicated direction when the middle
switch is in the LOCAL position.
Figure 2-1 DECtape Transport TU55 Block Diagram
2-1
Ir
REEL
RIGHT
LEFT
..
REEL

DECTAPE·TRANSPORT TU55
The SELECTOR LOGIC block in figure 2-1 includes the front panel thumbwheel selector
shown in figure 1-1. This selector has nine positions (designated 1 throU!3h 8 and OFF LINE) for selecting
one of eight select lines which are the outputs of a binary-coded-decimal decoder in the external DEC-
tape control system. During addressing, only one of the eight input select lines is at the asserted
ground. In remote operation, the SELECT output is asserted negative whenever the thumbwheel setting
corresponds to the asserted address I ine from the DECtape control system.
Writing is possible on a selected drive only when that drive furnishes control with a WRITE
ENABLE signal at ground. A selected TU55 furnishes such a signal when the WRITE ENABLE switch in
figure 2-1 is on. When this switch is set to WRITE LOCK, the output line is negative and writing can-
not take place. If the control is commanded to perform a write function when WRITE LOCK is selected,
it displays a selection error flag to notify the program of the mistake.
The five motion commands from the external DECtape control system are shown entering at
the left center. The ALL HALT signal is asserted negative by the externad control whenever the computer
program execution is halted either by the program or by the operator. When the program is halted, the
computer cannot issue commands to peripheral equipment. The ALL HALT signal stops those transports
thot were in motion at the time of the ALL HALT command, thus preventing a complete run-off of the
tape.
The other four commands, GO, STOP, FORWARD, and REVERSE, are asserted at ground by
the external control in response to computer program commands. In current DECtape controls, GO and
STOP are complementary levels. In the following discussion, the GO, STOP, FORWARD, and REVERSE
lines referred to are at the output of the signal interface module (BOl).
Tape motion begins at a selected TU55 when the GO line is asserted (STOP must be held
false throughout the desired interval of tape motion). Motion stops whenever the STOP I ine is asserted
while the GO line is simultaneously held false.
The same conditions as above apply to the FORWARD and REVERSE lines. For a selected
transport which is set to REMOTE, asserting the FORWARD line (while holding the REVERSE line false)
causes all subsequent remote GO commands to move tape forward. Sim i klrly, asserting the REVERSE
line (while holding the FORWARD line false) selects the reverse direction. In LOCAL operation, the
reverse and forward tape-motion switches override the last REMOTE direction command so that the tape
always moves in the direction of the arrow above the switch (see figure 2,-1).
Current DECtape controls generate the GO/STOP and the FORWARD/REVERSE signals as
complementary levels. Forward tape motion, for example, is commanded by assertion levels on GO and
FORWARD accompanied by false levels on STOP and REVERSE.
When forward motion is commanded either locally or remotely, the motion control logic asserts
the FWD output negative. This signal releases both brakes and applies full clockwise torque to the right
2-2

DECT APE TRANSPORT TU55
motor
and partial counterclockwise torque to the left motor. As a result the tape moves from the left
reel across the head onto the right reel. The REV I ine {asserted negative in response to the REVERSE
motion command} applies full torque to the left motor, partial torque to the right motor, and simulta-
neously releases both brakes. Tape motion, therefore, is from right to left. At the end of either com-
mand, the STOP I ine is asserted negative and triggers the stop delay {about 100 msec}. For the
duration of the delay, full torque is appl ied to the trail ing motor and stop torque is appl ied to the
I eading motor {see section 3. 3}. Thus, for the duration of the delay after the STOP command has
been issued, the motor torques are reversed causing tape movement also to be reversed. This time,
however, is very short and when the delay times out, the motors come to zero speed while changing
the ir rotation from one direction to the other. After the STOP DELAY times out, the tape becomes
motionless and partial torque is applied to both reels to take up the tape slack and the brake is applied
to the motor shaft which was trail ing during the previous motion. The effect of the delay is null ified
if a new motion command is given before the end of the l-sec interval. Then, the torque signals to the
left and right motor drives are immediately reestablished according to the new motion command. The
delay starts again at the leading edge of each STOP signal regardless of the frequency of its occurrence;
i.e., no recovery time is inherent in this type at delay.
An illustration of the tape head is shown in figure 2-2. Every channel consists of two tracks
associated with their coils. When writing, the current flows from ground {center tap} through one of
the coils {to either + or - terminal}to saturate the tape in one direction and through the other coil to
saturate the tape in the other direction. The coils for the two tracks are wired in series and are brought
out as four Iines: ground, +, -, and the shield. Within the head relay module, the +, -, and ground
lines {center taps} for a channel are switched by one of five 3-pole, normally open reed relays. Shields
are not switched, but are through-connected from the head to the interface connectors. A separate
line from the timing channel {also shown in figure 2-2} is brought out to allow measurements of head
skew {or the head perpendicularity}. This line isusedonly for test purposes (and not by the external
control). The single head-ground line is used to ground the head case.
2-3