IBM 1 Series - Processor I;O Channel Operational Characteristics; Operational Sequences on the Channel

Processor I/O Channel Operational Characteristics
Operational Sequences on the Channel
Operations on the processor I/O channel are performed by the following
major signal sequences, utilizing either the service group, the poll group, or
a combination of both:
DPC sequence (service group)—a write or read transfer initiated by
an Operate I/O instruction. The sequence terminates after one byte or
one word is transferred.
Interrupt-service sequence (service group)—initiated by a poll capture
following an interrupt request from an I/O device. The sequence is
terminated after the interrupt ID word is transferred.
Cycle-steal service sequence (service group)—an input or output
transfer initiated by a poll capture after a cycle-steal request from the
I/O device. The sequence terminates after one byte- or word-transfer
unless burst mode is active.
Poll sequence (poll group)— initiated by either an interrupt request or
a cycle-steal request. The poll is either propagated or captured by an
I/O device. If the poll is captured, the I/O device returns a ‘poll
return’ tag to indicate either (1) the capture of an interrupt poll or (2)
a single cycle-steal transfer. The device returns the ‘burst return’ tag
for multiple cycle-steal transfers.
Processor-initiated IPL sequence (service and poll group)— initiated
when the Load key on the console is pressed. The sequence terminates
when the I/O device has transferred the complete IPL record.
Host-initiated IPL sequence (service and poll groups)—initiated by a
signal from the I/O attachment that connects the I/O channel to the
host processor. The sequence terminates when the complete IPL
record has been transferred.
Reset sequences—(1) initiated by the ‘halt or MCHK’ tag when a Halt
I/O command is issued or when a machine-check interrupt occurs, or
(2) initiated when the system Reset key on the console is pressed.
Processor I/O Channel 2-15