or CLEAR I/O. Except for conditions associated
with command chaining and equipment malfunction
ing, the storing can be caused by the PCI or channel
end condition and by the execution of HALTI/O or
HALT DEVICE on the selector channel. The con
tents of theCSW are related to the current values of
the corresponding quantities, although the count isunpredietable after program check, protection check,
chaining check, and after an interruption due to the
PCI flag.
A CSW stored upon the execution of a chain of
operations pertains to the last operation thc channel
executed or attempted to initiate. Information con
cerning the preceding operations is not preserved
and is not made available to the program.
When an unusual condition causes command
chaining to be suppressed, the premature concluding
of the chain is not explicitly indicated in theCSW. A CSW associated with a concluding due to a condi
tion occurring at channel-end time contains the
channel-end bit and identifies the unusual condition.
When the device signals the unusual condition with
control unit end or device end, the channel-end indi
cation is not made available to the program, and the
channel provides the current protection key, com
mand address, and count, as well as the unusual indi
cation, with the control-unit-end or device-end bit in
theCSVv. The command address and count fields
pertain to the operation that wast1xecuted. When the execution of a chain of commands is
concluded by an unusual condition detected during
initiation of a new operation, the command address
and count fields pertain to the rejected command.
Except for conditions caused by equipment malfunc
tioning, concluding at the initiation time can occur
program check, and causes both the channel-end and
device-end bits in theCSW to be turned off.
A CSW associated with conditions occurring after
the operation at the sub channel has been concluded
contains zeros in the protection key, command ad
dress, and count fields, provided the conditions are
not cleared duringSTART I/O or START I/O FAST RELEASE and provided the logout-pending
condition is not indicated. These conditions include
attention, control unit end, and device end (and
channel end when it occurs after the concluding of
an operation on the selector channel by HALTI/O or HALT DEVICE).
When the above conditions, other than logout
pending, are cleared duringSTART I/O or START I/O FAST RELEASE, only the status portion of the CSW is stored, and the original contents of the pro
tection key, command address, and count fields in
location 64 are preserved. Similarly, only the status
236System/370 Principles of Operation
bits of theCSW are changed when the command is
rejected or the operation at the subchannel is con
cluded during the execution ofST ART I/O or START I/O FAST RELEASE or whenever HALT I/O or HALT DEVICE causes CSW status to be
stored.
Errors detected during execution of theI/O oper
ation do not affect the validity of theCSW unless
the channel-control-check or interface-control-check
conditions are indicated. Channel control check
indicates that equipment errors have been detected
which can cause any part of theCSW, as well as the
address in thePSW identifying the I/O device, to be
invalid. Interface control check indicates that the
address identifying the device or the status bits re
ceived from the device may be invalid. The channel
forces correct parity on invalidCSW fields.
When anyI/O instruction cannot be executed
because of a pending logout condition which affects
the operational capability of the channel or subchan
nel, a fullCSW is stored. The fields in the CSW are
all set to zeros, with the exception of the logout
pending bit and the channel-control-check bit, which
are set to ones.
Protection Key
ACSW stored to reflect the progress of an operation
at the subchannel contains the protection key used
in that operation. The contents of this field are not
affected by programming errors detected by the
channel or by the condition causing termination of
the operation.
Command Address
When theCSW is formed to reflect the progress of
theI/O operation at the subchannel, the command
address is normally eight higher than the address of
the last CCW used in the operation.
The following table lists the contents of the com
mand address field for all conditions that can cause
theCSW to be stored. The conditions are listed in
order of priority; that is, if two conditions are indi
cated or occur, theCSW appears as indicated for the
condition higher on the list. The programming er
rors listed in the table refer to conditions included in
program check. When aCSW has been stored and
the situation exists that a command retry request has
been recognized but the CCW has not been re
executed, "last-used CCW +8" is the CCW that is
to be retried.
Count
The residual count, in conjunction with the original
count specified in the last CCW used, indicates the
number of bytes transferred to or from the area des
ignated by the CCW. When an input operation is
with command chaining and equipment malfunction
ing, the storing can be caused by the PCI or channel
end condition and by the execution of HALT
HALT DEVICE on the selector channel. The con
tents of the
the corresponding quantities, although the count is
chaining check, and after an interruption due to the
PCI flag.
A CSW stored upon the execution of a chain of
operations pertains to the last operation thc channel
executed or attempted to initiate. Information con
cerning the preceding operations is not preserved
and is not made available to the program.
When an unusual condition causes command
chaining to be suppressed, the premature concluding
of the chain is not explicitly indicated in the
tion occurring at channel-end time contains the
channel-end bit and identifies the unusual condition.
When the device signals the unusual condition with
control unit end or device end, the channel-end indi
cation is not made available to the program, and the
channel provides the current protection key, com
mand address, and count, as well as the unusual indi
cation, with the control-unit-end or device-end bit in
the
pertain to the operation that was
concluded by an unusual condition detected during
initiation of a new operation, the command address
and count fields pertain to the rejected command.
Except for conditions caused by equipment malfunc
tioning, concluding at the initiation time can occur
program check, and causes both the channel-end and
device-end bits in the
A CSW associated with conditions occurring after
the operation at the sub channel has been concluded
contains zeros in the protection key, command ad
dress, and count fields, provided the conditions are
not cleared during
condition is not indicated. These conditions include
attention, control unit end, and device end (and
channel end when it occurs after the concluding of
an operation on the selector channel by HALT
When the above conditions, other than logout
pending, are cleared during
tection key, command address, and count fields in
location 64 are preserved. Similarly, only the status
236
bits of the
rejected or the operation at the subchannel is con
cluded during the execution of
stored.
Errors detected during execution of the
ation do not affect the validity of the
the channel-control-check or interface-control-check
conditions are indicated. Channel control check
indicates that equipment errors have been detected
which can cause any part of the
address in the
invalid. Interface control check indicates that the
address identifying the device or the status bits re
ceived from the device may be invalid. The channel
forces correct parity on invalid
When any
because of a pending logout condition which affects
the operational capability of the channel or subchan
nel, a full
all set to zeros, with the exception of the logout
pending bit and the channel-control-check bit, which
are set to ones.
Protection Key
A
at the subchannel contains the protection key used
in that operation. The contents of this field are not
affected by programming errors detected by the
channel or by the condition causing termination of
the operation.
Command Address
When the
the
address is normally eight higher than the address of
the last CCW used in the operation.
The following table lists the contents of the com
mand address field for all conditions that can cause
the
order of priority; that is, if two conditions are indi
cated or occur, the
condition higher on the list. The programming er
rors listed in the table refer to conditions included in
program check. When a
the situation exists that a command retry request has
been recognized but the CCW has not been re
executed, "last-used CCW +
to be retried.
Count
The residual count, in conjunction with the original
count specified in the last CCW used, indicates the
number of bytes transferred to or from the area des
ignated by the CCW. When an input operation is
