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CSW Status Stored by
SIO or
HIO or
I/O
Condition
SIOF;t
TIO
CLRIO+
HDV
IRPT#
Subchannel available
DE or attention in device
B,cl
NB,cl
*-
*-
NB,cl
Device working, CU available
B
B
*-
*-
B
CU end or channel end in CU:
for the addressed device
B,cl
NB,cl
NB
*-
NB,cl
for another device
B,SM
B,SM
NB
*-
NB,cl
CU working
B,SM
B,SM
NB
*-
B,SM
Interruption condition in
subchannel for the addressed
device because of:
chaining terminated by busy
*-
B,cl
NB,cl
*-
B,cl
other type of termination
*-
NB,cl
NB,cl
*-
NB,cl
Subchannel working
CU available
*-
*-
NB
NB
*-
CU working
*-
*-
NB
B,SM
*-
Explanation:
B
cl
CU
DE
NB
SM
#
Busy bit in CSW is one.
Interruption condition cleared; status is placed in CSW.
Control unit.
Device end.
Busy bit is zero.
Status-modifier bit appears in CSW.
CSW not stored, or I/O interruption cannot occur.
When a channel executes START I/O FAST RELEASE as START I/O, the
CSW
status
stored for the two instructions is identical.
When START I/O
FAST RELEASE is executed independently of the device, the same status
is stored by
an
I/O
interruption
with
the
CSW
also
indicating
deferred condition code 1.
Except
when
the
I/O interruption is caused by a deferred condition
code 1 for START I/O FAST RELEASE.
+
The entries in this column apply only
when
the
CLRIO
function
is
executed.
When CLEAR I/O causes the TIO function to be executed, the
entries in the TIO column apply.
Indications of Busy in CSW
Channel End
Channel end is caused by the completion of the
portion of an 110 operation involving transfer of
data or control information between the 110 device
and the channel. The condition indicates that the
subchannel has become available for use for
another operation.
Each 110 operation causes channel end to be
signaled, and there is only one channel end for an
operation. Channel end is not signaled when
programming errors or equipment malfunctions are
12-50
IBM 4300 Processors Principles of Operation
detected during initiation of the operation. When
command chaining takes place, only the channel
end of the last operation of the chain is made
available to the program. Channel end is not made
available to the program when a chain of
commands is prematurely concluded because of an
unusual situation indicated with control-unit end or
device end or during the initiation of a chained
command.
The instant within an 110 operation when
channel end is signaled depends on the operation
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