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Serial I/O Interface

According to Stan Paddock, both of "our" 1401 computers are equipped with a Serial I/O Interface. The Connecticut machine option was modified for extra voltages for the minicomputer interface.

The Serial Interfaces could communicate with devices such as paper tape readers, consoles, and even an IBM 7040 computer.

During a flurry of e-mails in August 2020, Lyle Bickley sent the following about an IBM 1401 to IBM 704x interface:
Attached is on OCRed Pri. of Ops. manual for the 704X (I always OCR bitsavers stuff). Size 7.4 MegaBytes, local, with OCR, BitSavers

There's what seems to me to be a pretty good explanation of how the 704X and the 1401 are connected and interact. Below is some of what's in the manual. You can search for 1401 to find the rest ;)

Pg 5
The basic 7040 or 7044 system includes one input- output channel, data channel A, whose operation is not overlapped with processing unit operation. IBM punched card equipment, output printers, magnetic tape units, on-line IBM 1401 Data Processing Systems, and Tele-processing equipment may be attached to this channel.

Pg 46
Data Channels
Channel A Devices
Input-output devices and control units that may be attached to channel A include one each of the following:

  1. One 1414-1, 2, or 7 Input-Output Synchronizer
  2. Up to three 1414-3, 4, 5, or 8 Input-Output Synchronizers, or 1622 Card lRead Punch.
  3. One 1401 Data Processing System
  4. One Console Typewriter (standard feature) Each of the above units, with the exception of the 1622 card read punch and the console typewriter, may have individual input-output devices attached. Limitations of the number of these devices is as later stated in the description of each device.
Pg 63-67
IBM 1401 Data Processing System
Any IBM 1401 Data Processing System and its input- output devices may be connected to data channel A by using the 1401 special feature Serial Input-Output Adapter (SF 7080). Except for input-output instructions, computer instructions of both systems operate normally.

To start an input-output operation, the 7040 or 7044 must be synchronized with the 1401 program. Synchronization is possible when the 1401 program is in a mode that enables it to respond to a 7040/7044 instruction. The 1401 informs the 7040/7044 that it is in this mode by executing the KE instruction. This instruction sets an indicator ( 1401 in loop) in channel A. When the 7040/7044 executes a TDOA instruction for the 1401, the indicator status determines if the program transfers (if the indicator is off, the program transfers ) .

When any select instruction ( RDS, WRS, CTR, BSR, WEF, REW, RUN) is directed to the 1401, that instruction causes the CPU to hang up if the in-loop indicator is off. If the indicator is on, the select instruction turns it off and sends a signal to the 1401. The 1401 program can sense this signal by executing the instruction B ( AAA) 2. If the signal is present, the 1401 branches to location ( AAA); if the signal is not present, the 1401 executes its next sequential instruction. A basic synchronization loop in the 1401 program could be:

LOCATION INSTRUCTION
X KE
X+2 B(AAA)2
X+7 B(X)

When the instruction at X + 2 branches, the 1401 program should proceed to a routine that selects its serial 1-0 adapter to read six bytes. When the serial 1-0 adapter is selected, the 7040/7044 transfers its entire select instruction (without change) to the 1401. The 1401 decodes this instruction to determine the operation and unit involved. If the unit is tape, reader...
Cheers,
Lyle
--
73 NM6Y
Bickley Consulting West
https://bickleywest.com

"Black holes are where God is dividing by zero"