Condition Channel control check
Status stored by START I/O or START I/O FAST RELEASE
Status stored by HALT I/O or HALT DEVICE Invalid CCW address specified in transfer in channel (TIC) Invalid CCW address in TIC Invalid CCW address generated Invalid command code Invalid count Invalid data address I nval id CCW format Invalid sequence - 2 TICs Protection check
Chaining check
Termination under count control Termination by I/O device
Termination by HALT I/O Termination by CLEAR I/O .,
Suppression of command chaining due to unit check or unit
exception with device end or control unit end
Termination on command chaining by busy, unit check, or
unit exception
Deferred condition code 1 for START I/O FAST RELEASE PCI flag in CCW I nterface control check Channel end after HALT I/O on selector channel Channel end after CLEAR I/O Control unit end
Device end
Attention
Busy
Status modifier
Contents of the CSW Command Address Field
concluded, the difference between the original count
in the CCW and the residual count in the CSW is
equal to the number of bytes transferred to main
storage; on an output operation, the difference is
equal to the number of bytes transferred to the I/O device.
The following table lists the contents of the count
field for all conditions that can cause the CSW to be
stored. The conditions are listed in the order of pri­
ority; that is, if two conditions ate indicated or oc­
cur, the CSW appears as for the condition higher on
the list.
Status
The status bits identify the conditions that have been
detected during the I/O operation, that have caused
a command to be rejected, or that have been gener­
ated by external events.
When the channel detects several error condi­
tions, all conditions may be indicated or only one
Contents of Field Unpredictable
Unchanged
Unchanged
Address of TIC + 8
Address of TIC + 8
First invalid CCW address + 8
Address of invalid CCW + 8
Address of invalid CCW + 8
Address of invalid CCW + 8
Address of invalid CCW + 8
Address of second TIC + 8
Address of protected COW + 8
Address of last-used CCW + Address of last-used CCW + 8
Address of last-used CCW + 8
Address of last-used CCW + 8
Address of last-used CCW + 8
Address of last CCW used in the completed operation + 8
Address of CCW specifying the new operation + 8
Address of CCW specifying the new operation + 8
Address of last-used CCW + 8
Unpredictable Zero Zero Zero Zero Zero Zero Zero may appear in the CSW, depending on the condition
and model. Conditions associated with equipment
malfunctioning have precedence, and whenever mal­
functioning causes an operation to be terminated,
channel control check, interface control check, or
channel data check is indicated, depending on the
condition. When an operation is concluded by pro­
gram check, protection check, or chaining check, the
channel identifies the condition responsible for the
concluding and mayor may not indicate incorrect
length. When a data error has been detected and the
operation is concluded prematurely because of a
program check, protection check, or chaining check,
both data check and the programming error are
identified.
If the CCW fetched on command chaining con­
tains the PCI flag but a programming error in the
contents of the CCW precludes the initiation of the
operation, whether the PCI bit appears in the CSW associated with the interruption condition is unpre­
dictable. Similarly, if a programming error in the
Input/Output Operations 237

Condition Channel control check
Status stored by START I/O or START I/O FAST RELEASE
Status stored by HALT I/O or HALT DEVICE Program check
Protection check
Chaining check
Termination under count control Termination by I/O device
Termination by HALT I/O or HALT DEVICE Termination by CLEAR I/O Suppression of command chaining due to unit check or unit
exception with device end or control unit end
Termination on command chaining by busy, unit check,
or unit exception
Deferred Gondition code 1 or 3 for START I/O FAST RELEASE PCI flag in CCW Interface control check Channel end after HALT I/O on selector channel Channel end after CLEAR I/O Control unit end
Device end
Attention
Busy
Status modifier Contents of the CSW Count Field
contents of the CCW causes the command to be
rejected during execution of START I/O or START I/O FAST RELEASE, the CSW stored by the in­
struction mayor may not contain the PCI bit. Fur­
thermore, when the channel detects a programming
error in the CAW or in the first CCW, the PCI bit
may unpredictably appear in a CSW stored by
START I/O or START I/O FAST RELEASE with­
out the PCI flag being on in the first CCW associat­
ed with the instruction. if the CCW fetched on command chain­
ing contains the PCI flag but an unusual condition
signaled by the device precludes the initiation of the
operation, the PCI bit appears in the CSW associat­
ed with the interruption condition. Likewise, if de­
vice status causes the command to be rejected during
execution of START I/O or START I/O FAST
RELEASE, the CSW stored by the instruction con­
tains the PCI bit.
Conditions detected by the channel are not relat­
ed to those identified by the I/O device.
The following table summarizes the handling of
status bits. The table lists the states and activities
that can cause status indications to be created and
the methods by which these indications can be
placed in the CSW.
238 System/370 Principles of Operation Contents of Field Unpredictable
Unchanged
Unchanged
Unpredictable
Unpredictable
Unpredictable
Correct
Correct
Unpredictable
Unpredictable
Correct. Residual count of last CCW used in the completed
operation.
Correct. Original count of CCW specifying the new operation.
Correct. Original count of CCW specifying the new operation.
Unpredictable
Unpredictable Zero Zero Zero Zero Zero Zero Zero Channel Logout
When a channel stores a CSW that indicates the
channel-control-check condition in the absence of
the logout-pending indication, or the interface­
control-check condition, or, on some channels, the
channel-data-check condition, a channel logout,
useful for error-recovery or diagnostic purposes,
accompanies the storing of the CSW. The logout
may be a limited channel logout, a full channel log­
out, or both. The type of logout that occurs and, for
the full logout, the length of the logout and the loca­
tion at which it is stored, depend on the channel type
and model number.
The limited channel logout contains model­
independent information and is stored at realloca­
tions 176-179 of the CPU to which the channel is
configured. When it is stored, bit 0 of the logout is
always stored as a zero.
The full channel logout contains model-dependent
information. When the length of the full channel
logout exceeds 96 bytes, it is stored at the location
specified by the I/O extended logout (IOEL) point­
er in reallocations 173-175 of the CPU to which the
channel is configured. When the length of the full
channel logout is 96 bytes or fewer, the channel may
either use the 10EL pointer or may store the logout
in the fixed-logout area, reallocations 256-351 of