IBM Series 1 User Manual page 34

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resolution in the channel or provide a system level
description. The IPL and reset sequences are of a special
nature. IPL sequences use the poll and service groups in
combination and involve operations with only one specific
device with no other device active. Resets are entirely
asynchronous and will affect operations on both groups.
The left-hand side of the diagram shows the poll group
resources. The right-hand side shows the service group
resources. The inputs to the "poll for interrupt" block on
the diagram are interrupt request and cycle steal request.
The only input that goes directly to the service group
resources is the Operate I/O instruction.
For example, assume an interrupt request becomes active
and gates the "poll for interrupt" block. This starts the
poll sequence. The poll sequence gates the "interrupt
acceptance" block, but inhibits cycle steal sequences,
DPe
sequences, and any further polling until this interrupt is
serviced.
As another example, assume the cycle steal burst
sequence is active. The diagram shows that this sequence
degates all other sequences. This is what is meant by
saying the I/O channel is totally dedicated to the I/O
device when in burst mode.
Processor I/O Channel 2-19