CONDITION Channel control check Status stored by START I/O Status stored by HALT I/O Invalid CCW address spec. in TIC Invalid CCW address in TIC Invalid CCW address
generated
Invalid command code
Invalid count
Invalid data address
Invalid CCW format
Invalid sequence -2 TIC's
Protection check
Chaining check
Termination under count
control
Termination by I/O device
Termination by HALT I/O Suppression of command
chaining due to unit check
or unit exception with de­
vice end or control unit end
Termination on command
chaining by attention, unit
check, or unit exception
Program-controlled interrup-
tion
Interface control check Ch. end after HIO on seI. ch.
Control unit end
Device end
Attention
Busy Status modifier
Count
CONTENT
Unpredictable
Unchanged
Unchanged
Address of TIC + 8
Address of TIC + 8
Address first invalid CCW + 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 invalid CCW + 8
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 last-used CCW + 8
Address of last-used CCW + 8 Zero Zero Zero Zero Zero Zero 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 desig­
nated by the ccw. When an input operation is termi­
nated, 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 out­
put 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 prior­
ity; that is, if two conditions are indicated or occur,
the csw appears as for the condition higher on the list.
CONDITION
Channel control check Status stored by START I/O Status stored by HALT I/O Program check
Protection check
Chaining check
Termination under count
control
Termination by I/O device
Termination by HALT I/O Suppression of command
chaining due to unit check,
unit exception with device
end, or control unit end
Termination on command
chaining by atention, by
unit check, or unit
exception
Program-controlled inter-
ruption
Interface control check Ch. end after HIO on sel. ch.
Control unit end
Device end
Attention
Busy Status Modifier
Status CONTENT Unpredictable
Unchanged
Unchanged
Unpredictable
Unpredictable
Correct
Correct
Correct
Correct
Correct. Residual count of last CCW used in the completed
operation.
Correct. Original count of CCW specifying the new
operation.
Unpredictable
Correct Zero Zero Zero Zero Zero Zero 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 generated
by external events.
The csw contains at least one status bit, unless it is
stored by HALT I/O issued to the multiplexor channel
or the interruption condition responsible for the stor­
ing is caused by HALT r/o issued to the selector chan­
nel. In both of the latter cases, all status bits may be
off.
When the channel detects several error conditions,
all conditions may be indicated or only one may ap­
pear in the csw, depending on the condition and
model. Conditions associated with equipment mal­
fU'hctioning have precedence, and whenever maHunc­
tioning 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 terminated by program check, pro­
tection check, or chaining check, the channel identifies Input/Output Operations 115
the condition responsible for the termination and may
or may not indicate incorrect length. When a data er­
ror has been detected before termination due to pro­
gram check, protection check, or chaining check, both
data check and the programming error are identified.
If the csw fetched on command chaining contains
the PCI flag but a programming error in the contents of
the csw or an unusual condition signaled by the de­
vice precludes the initiation of the operation, the PCI bit appears in the csw associated with the interruption
condition. Similarly, if device status or a programming
error in the contents of the ccw causes the command
to be rejected during execution of START I/O, the csw
stored by START I/O contains the PCI flag. The I/O flag,
however, is not included in the csw if a programming
error in the contents of the CAW prevents the oper­
ation from being initiated.
Conditions detected by the channel are not related
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.
TIME AND METHOD OF CREATING AND STORING STATUS INDICATIONS WHEN WHEN UPON TERMINATION OF OPERATION DURING BY BY BY BY I/O I/O IS SUB CHANNEL AT AT CONTROL AT COMMAND START TEST HALT INTER- STATUS IDLE WORKING SUBCIIANNEL UNIT DEVICE CHAINING I/O I/O I/O RUPTION ---------- Attention Co Status modifier
Control unit end
Busy
Channel end Co Device end Co Unit check C Unit exception C
Program-controlled interruption Co C
Incorrect length C C
Program check C C
Protection check C C
Channel data check Co C
Channel control check Co Co Co Interface control check Co Co Co Chaining check C C NOTES C-The channel or the 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.
Condition such as channel end and 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 are
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. S- The status indication is stored in the CSW at the indicated
time.
An S appearing alone indicates that the condition has been
created previously. The letter C appearing with the S indicates
that the status condition did not necessarily exist previously in
the form that causes the program to be alerted, and may have
116
C Co S S S C C CS CS CS S C1) CS CS CS S C CS CS CS S C1)H COt Ct S S S Co C l' C1' S s S C C Co CS CS CS C C Co CS S S C CS S S S S Co CS S S S S S S C1) Co Co CS CS CS CS C1) Co Co Cs CS Cs CS S S been created by the I/O instruction or I/O interruption. For
example, equipment malfunctioning may be detected during an I/O interruption, causing channel control check or interface
control check to be indicated; or a device such as the 2702 Transmission Control Unit 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 indi­
cated in the CSW. 1) -The status condition generates or, in the case of channel
data check, may generate an interruption condition.
Channel end and device end do not result in interruption
conditions when command chaining is specified and no unusual
conditions have becn detected. 1'- This status indication can be created at the indicated time
only by an immediate operation.
II-When an operation on the selector channel has been termi­
natcd by HALT I/O, channel end indicates the termination of
thc datu-hundling portion of the operation at the control unit.
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