An IBM 729 Tape Unit Refresher

Operator accessible - (can see indicator light, or operate key/switch/dial/... Other switches

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 key	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. 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. Effective only when the reel door is closed and the READY light is OFF. When tape is properly mounted in the tape unit at the beginning of a job, pressing this key 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. 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. 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: 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. Pressing the key makes all other keys, except RESET, inoperative.
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	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 It is effective only when the reel door is closed and the READY light is OFF.
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 / HIGH 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 Sensing the end-of-reel reflective marker during a tape-writing operation. Reading a tape mark during a tape-reading operation. this light is turned OFF by pressing UNLOAD, or by executing a REWIND TAPE AND UNLOAD or BRANCH IF END OF REEL program instruction.
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.
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.

For "Operations" such as loading tape, see A24-3144-2 "IBM 1401 Operator's Guide" page 70

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