An IBM 729 Tape Unit Refresher
Collected by Ed Thelen
1401 Tape-Adapter Unit (TAU) Commands (software)
Operator accessible keys, switches, lights
200 pin signal cable
D.C. Power Requirements
Possible 729 Tape Test Controller
There is a 729 tape manual at http://bitsavers.trailing-edge.com/pdf/ibm/magtape/729/223-6845_729_CEman_1959.pdf
A24-3069-2 says that the 1401 can use the following 729 Magnetic Tape Units - II, IV, V, VI although the 729 - VI operates at 729 IV speeds only.
A24-3067-2 System Operation Reference Manual
A24-3144-2 Operator's Guide,
page 63 starts the "IBM 729 and IBM 7330 Magnetic Tape Units"
- as many as six tape units can be attached to the system
- All tape units in the system must be the same model, unless the tape-intermix special feature is installed.
- all models of the IBM 729 and IBM 7330 have dual density.
- Density is controlled by a key (729) ... on the tape unit
* Density and Character Rate affected by Tape Density Switch
729II 729IV 729V* Density - Low ->
(Characters per inch)
(Inches per Second)
75 112.5 75 Interrecord Gap Size
3/4 3/4 3/4 Character Rate - Low Dens->
Characters per second)
1.2 .9 1.2 Regular Rewind
(Inches per Second)
75 112.5 75
- on 1401 Auxiliary Console.
- Characters are recorded on tape in binary-coded decimal (BCD) code, the same code as used in core storage.
- An interrecord gap, followed by a special single-character record known as a tape mark, is used to mark the end of a file of information.
- Reflective markers are placed on the tape, to mark the beginning and the end of the usable portion of tape.
Photoelectric cells recognize load-point marker (where reading or writing is to begin)
- or and end-of-reel marker (where the writing is to stop).
- The tape unit does not recognize the end-of-reel marker when reading tape. Instead, the tape mark written on the tape signals an end-of-reel condition.
- The markers are small pieces of transparent plastic with a thin film of aluminum on one side.
- Load-Point Marker - At least 10 feet of tape must be allowed between the beginning of the real and the load-point marker - placed parallel to and not more than 1/32" from the edge of the tape nearest the operator, then the reel is mounted.
- End-of-Reel Marker more than 14 feet from the end of the tape. (ten feet of leader and enough tape to hold a record of 9600 characters after the end-of-reel marker is sensed - away from the operator, when the reel is mounted.
- Tape Reels - 10.5" in diameter, holds 2400 feet of tape - (a 2400 foot reel can contain about 13 million characters, assuming records 2,000 characters in length, written at 556 characters per inch.)
- Each reel is equipped with a file-protection ring to safeguard data written on the tape. fits into the groove in the back (machine side) of the reel - no ring - no write
- Reel-Release Button - below the left-hand tape reel - It must be held pressed to turn either tape reel by hand.
- REEL DOOR - Interlock prevents any automatic or key-controlled operation when this door is open. This door should never be opened when the READY light is ON or curing load, rewind, or unload operation. With the door open during any of these operations, the tape could become damaged.
- "File Reel" is on the left, the "take-up" reel is on the right
- The upper half of the Read/Write Head Assembly pivots
- - up (open) when the UNLOAD is pressed
- or after a REWIND TAPE AND UNLOAD program instruction
- which also unloads the vacuum columns
- and must be open before opening the reel door to make manual adjustments
- - down (normal) after the LOAD REWIND key is pressed
- which also loads the vacuum columns
The 720 uses a two-gap write/read head to enable on-line check while writing data. There also seems to be erase head logic.
The Tape-Adapter Unit (TAU)
1401 Tape-Adapter Unit (TAU) Commands (software)
Read Tape - The tape unit specified in the A-address is started. The d-character specifies a tape read operation. The B-address specifies the high-order position of the tape read-in area of storage. the machine begins to read magnetic tape, and continues to read until either an inter-record gap in the tape record or a group-mark with a word-mark in core storage is sensed. ... Read tape with Word Marks - Write Tape - Write Tape with Word Marks - Backspace Tape Record - Skip and Blank Tape - erases about 3.5 inches of tape (bypass defective tape areas) Write Tape Mark - causes a tape mark character (8421) to be recorded - when a tape mark is read back from a tape, the end-of-reel indicator is turned on. (may actually be end of file, with more records yet on the tape) Diagnostic Read - reposition tape to next Inter-record gap (IRG) with no data transfer. Rewind Tape - Rewind Tape and Unload - Branch if End of Reel - Branch if Tape Error -
Operator accessible keys, switches, lights
Address Dial lights->SELECT READY LOW D | HIGH D ? TAPE
INDICATE | FUSE
" keys->LOAD REWIND START CHANGE DENSITY UNLOAD RESET
Operator accessible - (can see indicator light, or operate key/switch/dial/...
For "Operations" such as loading tape, see A24-3144-2 "IBM 1401 Operator's Guide" page 70
Name Physical Function ADDRESS SELECTION DIAL Assigns a number to the tape unit, to associate the unit with the tape-drive number specified in the stored program. Because a maximum of six tape units can be attached to the system, this dial may be set at any number 1-6. If some other number (7,8,9,0, or blank) is selected, the tape unit cannot be used by the stored program. A dial setting of any unit should never be changed while a tape operation is in process. Panel Keys and Switches LOAD REW LOAD REWIND
This key rewinds tape onto the file reel to its starting point (load point) It is used at two main times in any tape operation.
Effective only when the reel door is closed and the READY light is OFF.
- At the beginning of a job, to position the tape for reading or writing the first record.
- At the completion of a job, to rewind all tape onto the file reel ready for unloading.
When tape is properly mounted in the tape unit at the beginning of a job, pressing this key
When a job is completed, pressing this key rewinds tape from the take-up reel to the file reel until the load-point reflective marker is sensed. For this operation a low-speed rewind is initiated if the take-up reel contains less than one-half inch of tape (less than 450 feet). Else, a high-speed rewind (an average of 500 inches per second) is initiated.
- Lowers (loads) tape into the vacuum columns
- Closes the Read/Write Head Assembly
- Moves the tape to the left (rewind direction) until the load-point reflective marker is sensed. If the tape was mounted with the marker erroneously positioned to the left of the head assembly, the tape will unwind from the take-up reel.
Whenever this key has been pressed, the reel door must remain closed until the rewind operation is completed. If it were opened, the tape could be broken or damaged START key This key readies the tape unit for automatic operation, and turn ON the READY light. It is effective only when:
Pressing the key makes all other keys, except RESET, inoperative.
- The reel door is closed,
- Tape is loaded in the vacuum columns, and
- Tape is not in the process of loading or rewinding to the load point If START is pressed during a rewind operation, the READY light turns ON when rewinding is completed.
CHANGE DENSITY key Pressing this key changes the density rate of the tape unit from its previous setting (from low to high, or from high to low). the density rate in effect is indicated by the LOW DENSITY or HIGH DENSITY light, and must agree with the density rate of the tape being processed. This key is effective only when the READY light is OFF. UNLOAD key
It is effective only when the reel door is closed and the READY light is OFF.
- Opens the head assembly.
- Unloads the vacuum columns. If the tape has not been rewound to the file reel, the LOAD REWIND key should be pressed before UNLOAD
- Turn OFF the TAPE INDICATE light, if it is ON
RESET key This key changes the tape unit from automatic to manual control (making the other keys operative< and turn OFF the READY light.
This key also stops any machine operation in process, except unload or rewind. Once started, an unload operation is always completed. If a high-speed rewind is in process when RESET is pressed, rewinding shifts to low speed. If a low-speed rewind is in process, RESET stops the operation.
Panel Lights SELECT light When the tape unit is under automatic control (READY light ON), the yellow SELECT light turns ON whenever processing selects this unit for a tape operation. This is determined by the execution of a tape program instruction that contains the number of this unit (as set up in the address selection dial). READY light This light indicates that the tape unit is ready for automatic operation. It is turned ON by pressing the START key. When READY is lighted, all keys except RESET are inoperative. This light is turned OFF, and the tape unit is placed under manual control, by pressing the RESET key. The reel door should never be opened when the READY light is ON. LOW Density /
wire & light These lights indicate the density rate (low or high) in which the tape unit is operating. This must agree with the density rate on the tape being processed. HIGH DENSITY turn ON when power is initially turned ON in the system. The density rate can be changed to low by pressing the CHANGE DENSITY key. The red LOW DENSITY light turns ON. Each time this key is pressed (with the READY light OFF) the density rate is switched from its previous setting. FILE PROTECT light When this light is ON, i indicates that the tape in this unit can be read but not written on, because a tape reel without a file-protection ring has been mounted. This light also turn ON when no file reel is mounted, when a load, rewind, or unload operation is in process, or when the machine is under manual control (READ light OFF). TAPE INDICATE light This light is turned ON by
this light is turned OFF by pressing UNLOAD, or by executing a REWIND TAPE AND UNLOAD or BRANCH IF END OF REEL program instruction.
- Sensing the end-of-reel reflective marker during a tape-writing operation.
- Reading a tape mark during a tape-reading operation.
FUSE light This red light turns ON whenever a fuse or circuit breaker in the tape unit is open. The IBM customer engineer should be called to correct this condition. Other switches WRITE ENABLE SWITCH Push switch behind File Reel if depressed by the write Enable Ring on the tape reel, permits write to tape - no ring, no write - REEL RELEASE SWITCH Button It must be held pressed to turn either tape reel by hand. REEL DOOR Slide door Interlock prevents any automatic or key-controlled operation when this door is open. This door should never be opened when the READY light is ON or curing load, rewind, or unload operation. With the door open during any of these operations, the tape could become damaged. Other METER SWITCH switch? If the use-meter switch is not set to ON or the tape unit is not ready before an instruction calls on this unit, the system interlocks and the processing use-meter continues to run. METER TIME meter? Starts when the first tape operation affecting the particular tape unit is issued. The meter stops when the tape unit receives and completes a rewind unload command. The meter can be stopped by manually unloading the unit, or by pressing and releasing the RESET key.
in T/C connector receptacle
C.E. Manual has usage on page C77
Pin Name to/from Comments, Interpretation 1 Turn on T.I. terminator +1.5v @ 90 ohm 3 Turn off T.I. terminator -7.5v @ 90 ohm 5 Go terminator -7.5v @ 90 ohm 7 BKWD terminator +1.5v @ 90 ohm 9 Start Rewind terminator +1.5v @ 90 ohm 11 Set Write Status terminator +1.5v @ 90 ohm 13 Set Read Status terminator -7.5v @ 90 ohm 17 Spare terminator +1.5v @ 90 ohm 19 Spare terminator +1.5v @ 90 ohm 21 Sel & Rdy Mod IV 23 Sel & T.I. On 25 Sel & T.I. Off 27 Sel & at Ld. Pt. 29 Sel & not at Ld. Pt. 31 Sel & Rdy Mod II 33 Sel Rdy & Read 35 Sel Rdy & Write 37 Sel & Rewind 39 Rewind & Unload terminator -7.5v @ 90 ohm 41 Set Hi-Density terminator -7.5v @ 90 ohm 43 Set Lo-Density terminator +1.5v @ 90 ohm 47 Hi-Density Lo-Density 77 Sel T.U. 0 terminator -7.5v @ 90 ohm 79 Sel T.U. 1 terminator -7.5v @ 90 ohm 82 Read Bus 1 84 Read Bus 2 86 Sel T.U. 2 terminator -7.5v @ 90 ohm 88 Sel T.U. 3 terminator -7.5v @ 90 ohm 93 Read Bus 4 95 Read Bus 8 97 Sel T.U. 4 terminator -7.5v @ 90 ohm 99 Sel T.U. 5 terminator -7.5v @ 90 ohm 102 Read Bus A 104 Read Bus B 106 Sel T.U. 6 terminator -7.5v @ 90 ohm 108 Sel T.U. 7 terminator -7.5v @ 90 ohm 113 Read Bus C 117 Sel T.U. 8 terminator -7.5v @ 90 ohm 119 Sel T.U. 9 terminator -7.5v @ 90 ohm 132 + 6 V probably terminator supply power @ 200 ma 140 - 6 V probably terminator supply power @ 200 ma 170 - 12 V probably terminator supply power @ 200 ma 172 Write Bus 1 terminator +1.5v @ 90 ohm 174 Write Bus 2 terminator +1.5v @ 90 ohm 176 Write Bus 4 terminator +1.5v @ 90 ohm 178 Write Bus 8 terminator +1.5v @ 90 ohm 180 Write Bus A terminator +1.5v @ 90 ohm 182 Write Bus B terminator +1.5v @ 90 ohm 184 Write Bus C terminator +1.5v @ 90 ohm 192 Write Echo Pulse 194 Write Check Char terminator +1.5v @ 90 ohm 196 Write Pulse terminator +1.5v @ 90 ohm
From Customer Engineering Manual of Instruction
D.C. Power Requirements
Page C30 - from a single phase
Voltage Amp Use +6 1.5 Transistor logic circuits -6 1.5 Transistor logic circuits +12 1.0 Transistor logic circuits -12 1.0 Transistor logic circuits -7.5 20.0 Prolay driver circuits +73 0.165 Transistor neon indicator circuits -48 2.0 Relay circuits +140 5.1 Magnetic clutch circuit
First some locations
Circuit Protector Chart 00.05.1 530039 Relays 00.06.1, sheet 1 of 1 8021369 Keys, switches, lamps, pots 00.06.1, sheet 2 of 2 8021593 Pre-amps, Card Frame, Power transistors 00.07.1 530055 Neon panel 00.08.1 8015987 Write amps, Read Pre-amps 00.09.1 530057 Relay gate & Blowers 00.11.1 8021589 Power Transistor Panel 00.13.1 8012810 Voltage Bus +-6, +-12 00.15.1 526208
in 00.04.2, 8021590 - Component Location CLUTCH FILTER BOX Pot 1 Pot 2 Pot 3 Pot 14 VARIABLE CLUTCH CONTROL ASM (machines with JT. ?2982 L. STOP L. DOWN L.UP RT. DOWN RT. UP RT. STOP Relay gate & Blowers Pot 1 Pot 2 Pot 3 Pot 8 Clutch & Vacuum Control - 02.02.2 - 8018346 Pot 13 250 ohm, 25 watt Pot 12 250 ohm, 25 watt Pot 8 250 ohm, 50 watt Pot 11 250 ohm, 25 watt Pot 10 250 ohm, 25 watt Pot 3 5K ohm, 25 watt Pot 9 250 ohm, 50 watt
Possible 729 Tape Test Controller.I've been doodling with the idea of making a 729 tape test controller - to help check out 729s before and maybe after the 1401 comes up. There is the thought that the extra work in building a tape test controller would a) aid in bringing up the 729s sooner. b) help identify if problems are in - the 1401 controller - the 729 tape unit - cables/plugs c) permit parallel bring-up of 729 interface electronics with other components such as the 1401 (Quite a bit of the 729 can be tested/brought up with out any outside simulation equipment including - power supplies - blowers - read/write head assembly movement - prolay operation - tape movement - vacuum column operation - reel clutches and logic - load-point and end-of-tape detection - load, unload operations - reset/ready/tape density/... logic .) A down side is of course, - development time and resources, including a required T/C plug or socket - errors in the test controller :-(( Presumably the tape test controller could be based on a PC except that other aids may be necessary to - provide more exact and reliable timing than is available in the usual PC Ballistic Research Labs mentions tape data transfer rates of " 15,000 to 62,500 Char/sec " which may be within the raw transfer rate, but probably not delivered within the timing constraints needed. - provide the large number of digital inputs and outputs at suitable voltage and strength levels. I have done some slower, non-time critical digital interfacing but the apparent write data and write clocks There is a limited amount of information that I have noticed: a) signal names and 3 dc voltages through the "T/C connector receptacle" are identified in the 729 schematics on page 530035 - 00.021 and now at http://www.ed-thelen.org/1401Project/729-signals.html b) (Al Kossow's documentation web site www.bitsavers.org seems down right now.) There appear to be several challenges, including 729 items a) signal sequences and timings to/from the 729 are not obvious from the schematics b) expected voltages need to be worked out c) direction of signals (or bi-directionality) needs to be worked out. d) it would appear that the tape unit has a minimum amount of logic, and that the controller in the 1401 provides a large new test controller items ( amount of timing and sets a wide interface of signals
Updated July 16, 2016