to storage; on an output operation, the difference is equal to the number of
bytes transferred tothe I/O device.
The residual count, in conjunction with
the original count specified in the lastCCW used, indicates the number of bytes
transferred to or fromthe area desig
nated by theCCW. When an input opera
tion is concluded, the difference
between the original count in theCCW and the residual count in the CSW is
equal to the number of bytes transferredThe figure "Contents of the Count Field
in theCSW" lists the contents of the
count field for all situations that can
cause theCSW to be stored. They are listed in the order of priority; that
is, if two situations occur, theCSW appears as for the situation higher on
the list.
SituationsI/O instruction issued when
channel logout-pending
Channel-control check
Status stored by STARTI/O or
STARTI/O FAST RELEASE
Status stored by HALTI/O or
HALTDEVICE Program check
Protection checkChaining check
Termination under count control
Termination byI/O device
Termination by HALTI/O or
HALTDEVICE Termination by CLEAR I/O Suppression of command
chaining due to unit check,
attention, or unit exception
with device end, channel end,
or control-unit end
Termination on commandchaining by busy, attention, unit
check, or unit exception
Deferred condition code 1 or 3PCI flag in CCW Interface-control check Channel end after HALT I/O or
HALTDEVICE on selector chan
nel (and, depending on design
of the subchannel, on block
multiplexer channel)Channel end after CLEAR I/O Control-unit end Device end Attention
Busy
Status modifier
Channel-available interruptionContents of Field
Zero
Unpredictable
Unchanged
Unchanged
Unpredictable
Unpredictable
UnpredictableCorrect Correct Unpredictable
UnpredictableCorrect. Residual count of last CCW used in the completed
operation.Correct. Original count of CCW specifying the new
operation.
Unpredictable
Unpredictable
Unpredictable
Zero
Zero
ZeroZero Zero Zero Zero Zero Contents of the Count Field in the CSW Chapter 13. Input/Output Operations 13-77
bytes transferred to
The residual count, in conjunction with
the original count specified in the last
transferred to or from
nated by the
tion is concluded, the difference
between the original count in the
equal to the number of bytes transferred
in the
count field for all situations that can
cause the
is, if two situations occur, the
the list.
Situations
channel logout-pending
Channel-control check
Status stored by START
START
Status stored by HALT
HALT
Protection check
Termination under count control
Termination by
Termination by HALT
HALT
chaining due to unit check,
attention, or unit exception
with device end, channel end,
or control-unit end
Termination on command
check, or unit exception
Deferred condition code 1 or 3
HALT
nel (and, depending on design
of the subchannel, on block
multiplexer channel)
Busy
Status modifier
Channel-available interruption
Zero
Unpredictable
Unchanged
Unchanged
Unpredictable
Unpredictable
Unpredictable
Unpredictable
operation.
operation.
Unpredictable
Unpredictable
Unpredictable
Zero
Zero
Zero