IBM System/360 Field Engineering Manual

1/0 INTERFACE FLOW CHARTI>
Initiation of Polling or Selection
The start-poll decision
is usually made on the
basis of request in being
up.
Request in is raised when
a control unit has a need
for servicing and is
dropped when the need
is serviced.
The channel normally
services all requests
before initiating a
selection sequence
[
A3
A6
AB
(Ch)
Has Sel
Been Down,
it least
.5 usec
Yes
At decision blocks involving signal
lines, the question to be resolved
is-- Is the line logically up.
The presence of Ch (channel) or
CU (control unit) in a block,
specifies responsibility for the
action taken or decision made
Yes
All mention of select out
assumes proper operation of
hold out as well. Thus, select
out up means select out and
hold out up, and select out
down means either select out
or hold out down
A polling sequence or an initial selection
sequence has been started by the channel
IBM CONFIDENTIAL
S/360 115

IBM System/360 Specifications

General

Brand	IBM
Model	System/360
Category	Desktop
Language	English