IBM System/360

Control Unit Response to Select-Out
A control unit may be busy either
because it is busy operating a device
or because the control unit is
Note
holding status
(CU)
unable to execute
a command at th is
time and hence
initiates a control
unit busy sequence
(CU)
The control unit
acknowledges a
chcmnel-initiated
selection sequence
Status Byte
to Bus In
Raise
Operational In
Note
(CU)
Raise
Status In
A control unit
busy is now
indicated
Note: The byte on bus in must
be valid within 100 ns
after raising the in tag.
116
S/360
(CU)
Device Address
to Bus In
C3
The control unit has responded to
the select-out poll or addressing.
The channel must now examine the
response to determine whether to
abort the poll or selection, respond
to the control unit busy
1
or continue
with the sequence begun by
operational in
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