Programming instructions

INFORMATION DISTRIBUTOR (ID)
The Information Distributor presents the static data contained in the AC
to each output device requiring AC information. The devices sample the
Information Distributor using the program-controlled pulses from the
Device Selector. The program steps for transmitting information from a
particular memory cell are:
lac Y Load the AC with C(Y)
iot
Clear selected output register to prepare for information
iot transmit The information is sampled and placed in the register of the
input-output device.
(the second two steps may be microprogrammed together
in one instruction)
INPUT- OUTPUT SKIP FACILITY (10s)
The Input-Output Skip facility enables the program to skip (or branch)
according to various external device states. There are eight inputs to the
Skip facility. The iot pulses from the Device Selector strobe an input line
and if a logic condition is present, the instruction following the iot is skipped.
The iot skip pulse must occur at event time 1.
PROGRAM INTERRUPT CONTROL (PIC)
The program interrupt allows a logic line state to interrupt the program.
It is used to speed the processing of input-output device information, or
to allow certain alarm conditions to be sensed by the computer. The in-
terrupt may be enabled or disabled by the program.
When the interrupt occurs, the contents of the Program Counter and the
Link are stored in memory location 0 (bits 0, 5. . . 17) and an interrupt
program begins in memory location 1. This action disables the interrupt
mode. The interrupt program is responsible for finding the signal causing
the interruption, for removing the condition, and for returning to the
original program.
When the condition for interruption is removed, an iot signal to re-enable
the Program Interrupt is given, followed by the instruction, jmp indirect 0,
or 620000. The interrupt program will then resume. If a Program Interrupt
request is waiting, it will be serviced after the 620000 instruction. If a
second interruption condition occurs and the Interrupt program is running,
the signal will have no effect; that is, there is only one level of interruption.
The START key disables the Program Interrupt system. The iot instructions
for the program interrupt are:
iof - 700002 - Disable the Program Interrupt
ion - 700042 - Enable the Program Interrupt
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