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

Upon Termination
When
of Operation at
During By I/O Subchannel Sub- Control I/O Command By SIO By By HID Inter- Status
When I/O Is Idle is Working channel Unit Device Chaining or SIOF ByTIO CLRIO+ or HDV ruption
Attention
Status modifier C* Control unit end C* Busy Channel end C* C*H Device end C* Unit check C C C Unit exception
Program-controlled
interruption C* C C C* Incorrect length C C Program check C C Protection check C C Channel data check C C Channel control check C* C* C* C* I nterface control check C* C* C* C* Chaining check C C Deferred condo code 1
Deferred condo code 3
Explanation: C S The channel or device can create or present the status
condition at the indicated time. A CSW or its status
portion is not necessarily stored at this time.
Conditions such as channel end or device end are
created at the indicated time. Other conditions may
have been created previously, but are made accessible to
the program only at the indicated time. Examples of
such conditions are program check and channel data
check, which are detected while data is transferred, but
are made available to the program only with channel end,
unless the PCI flag or equipment malfunctioning have
caused an interruption condition to be generated earlier.
The status indication is stored in the CSW at the
indicated time.
An appearing alone indicates that the condition has
been created previously. The letter.f. appearing with the indicates that the status condition did not necessarily
exist previously in the form that causes the program to be
alerted, and may have been created by the I/O instruetion
or I/O interruption. For example, equipment malfunctioning may be detected during an I/O interruption, causing
channel or interface control check to be indicated; or a
device such as the 2702 may signal the control-un it-busy
condition in response to interrogation by an I/O instruction,
causing status modifier, busy, and control unit end to be
indicated in the CSW. Contents of the CSW Status Fields
the CPU to which the channel is configured. The
information stored by the STORE CHANNEL ID
instruction implies whether the IOEL is used and, if
it is used, specifies the maximum full-channel-logout
length. C* C C* C C C* C* #
H
+ C* S S S S C CS CS S CS S CS CS S CS S C CS CS S CS S C*+ CS+ S S S C+ CS+ S S S C* CS CS S CS C* CS S S S C CS S S S S S S C* CS S S S C* CS S S S S S S C* CS CS CS CS CS C* CS CS CS CS CS S S S C*# S S S C*# S S S The status condition generates an interruption condition. Channel end and device end do not result in interruption
conditions when command chaining is specified and no
unusual conditions have been detected.
This indication is created at the indicated time only by
an immediate operation. Applies only to SIOF. When an operation on the selector channel has been
concluded by HALT DEVICE or HALT I/O, or an
operation has been concluded by CLEAR I/O, channel
end indicates the concluding of the data-handling portion
of the operation at the control unit.
The entries in this column apply only when the CLRIO function is executed. When CLEAR I/O is executed as
TEST I/O, the entries in the TIO column apply. 110 Communications Area
Reallocations 160-191 of the CPU to which the
channel is configured comprise a permanently as­
signed area of main storage used for I/O, designated
the I/O communications area (lOCA). Input/Output Operations 239