July 11, 1962

{My copy of PMM 10 has sections 1 & 2 but is missing 3,4 and 5.}


Section 1 Brief description of the control of a peripheral by the computer.

Section 2 Summary of all wires between a peripheral control and the compute

Section 3 Permissible loading and required drive on all connecting lines.

Section 4 Standard Pin Connector for all Computer-Control Unit wires.

Section 5 Designated meaning to each peripheral state bit on read and
write buses.

1. Operation

Warning - This description is generalised and may not be applicable to
any given peripheral.

A transfer to or from a peripheral is initiated by the
executive following an order.

The executive interrogates the state of the peripheral via
executive select and the read bus (see sec. 5 for details). The write
buses are all zero at this time. The interrogation will also take place
at the request of a peripheral when the control unit raises "peripheral

The executive sends "start" to the peripheral using executive
select and the write bus (see sec. 5).

Executive plays no further part in the proceedings until the
peripheral alerts it with "Peripheral Incident."

The peripheral raises "Hesitation Request" when it has found
the information or is ready to receive it.

The computer sends "Hesitation Select" informing the peripheral
that the "reset",- "stop", and "Parity Fail" buses now apply to it#

Data is read or available when "reset" is raised.

"Hesitation Request" should now be dropped (releasing
"Hesitation Select") and raised again for the next word or character.

{page break} -2-

If the computer decides that the transfer is complete,
"stop” will be raised the bit before “reset", and for incorrect
transfers “Parity Fail" will be raised the bit after "Reset".

“Stop" will always be sent by the computer after 128
characters from a slow peripheral or 512 worms from a fast peripheral.

The peripheral should inform Executive of any unusual
conditions, i.e. Parity Fail, Stop etc. via "peripheral incident."

2. Signals

The following list is a complete list of all standard wires
connecting any peripheral control to the computer. The preceding
sign indicates polarity when activated, or a "one."

2.1 Computer to control unit


- Write bus 24 and parity

± Select bus 12 (64 selections)

- Stop Bus

- Reset Bus


+ Freeze

Lines (individual to peripheral)

+ Hesitation select I/P

+ Hesitation select O/P

2.2 Control Units To Computer


+ Read bus 24 and parity


+ Hesitation request I/P

+ Hesitation request O/P