channel end, control end, or device end. Such unit
status indicates that no action has bcen taken at the
device in response to the command. If the condition
precluding normal execution of the operation occurs
after the execution has been started, unit exception is
accompanied by channel end, control unit end, or de
vice end, depending on when the condition was de
tected.
Termination of an operation with the unit-exception
indication causes command chaining to be suppressed.Channel Status Conditions The following conditions are detected and indicated by
the channel. Except for the conditions caused by equip
ment ma1functioning, they can occur only while the
subchannel is involved with the execution of anI/O operation.
Program-Controlled Interruption
The program-controlled-interruption condition is gen
erated when the channel fetches a ccw with thepro gram-controlled-interruption (PCI) flag on. The inter
ruption due to thePC! flag takes place as soon as
possible after fetching the ccw but may be delayed an
unpredictable amount of time because of masking of
the channel or other activity in the system.
Detection of thePCI condition does not affect the
progress of theI/O operation.
Incorrect Length
Incorrect length occurs when the number of bytes con
tained in the storage areas assigned for theI/O oper
ation is not equal to the number of bytes requested or
offered by theI/O device. Incorrect length is indicated
for one of the following reasons:l.Jong blocl( on Input: During a read, read-backward,
or sense operation, the device attempted to transfer
one or more bytes to storage after the assigned storage
areas were filled. The extra bytes have not been placedin main storage. The count in the csw is zero. IJong Block on Output: During a write or control
operation the device requested one or more bytes from
the channel after the assigned main-storage areas were
exhausted. The count in the csw is zero.Short Block on Input: The number of bytes trans
ferred during a read, read hackward, or sense oper
ation is insufficient to fill the storage areas assigned to
the operation. The count in the csw is not zero.Short Block on Output: The device terminated a
write or control operation before all informationcon tained in the assigned storage areas was transferred to
the device. The count in the csw is not zero.
The incorrect-length indication is suppressed when
112
the current ccw has theSLI flag and does not have the CD flag. The indication does not occur for immediate
operations and for operations rejected during the ini
tiation sequence.
Presence of the incorrect-length condition suppresses
command chaining unless theSLI flag in the ccw is on
or unless the condition occurs in an immediate oper
ation.
The following table lists the effect of the incorrect
length condition for all combinations of theCD, CC, and SLI flags. It indicates for the two types of oper
ations when the operation at the sub channel is termi
nated (stop) and when the command chaining takes
place. The entry"incorrect length" (IL) means that
the indication is made available to the program; a
double hyphen (--) means that the indication is sup
pressed. For all entries, the current operation is as
sumed to have caused the incorrect-length condition.
FLAGS ACTION AND INDICATION
CD CCSLI HEGULAB OPEBA TION IMMEDIATE OPEHATION 0 0 0 Stop,IL Stop, -- 0 0 1 Stop, --Stop, -- 0 1 0 Stop,IL Chain command 0 1 1 Chain command Chain command
10 0 Stop,IL Stop, --
I0 1 Stop,IL Stop, --
I 10 Stop,IL Stop, --
I 1 1 Stop,IL Stop, --
Program Check
Program check occurs when programming errors are
detected hy the channel. The condition can be due to
the following causes:
Invalid C CWAddress Specification: The CAW or the
transfer-in-channel command does not designate the
ccw on integral boundaries for double words. The
three low-order bits of the ccw address are not zero.
Invalid CCWAddress: The channel has attempted
to fetch a ccw from a location outside the main stor
age ofthe particular installation. An invalid ccw ad dress can occur in the channel because the program
has specified an invalid address in theCAW or in the
transfer-in-channel command or because on chaining
the channel has stepped the address above the highest
available location.
Invalid Command Code: The command code in the
first ccw designated by theCAW or in a ccw fetched on
command chaining has four low-order zeros. The com
mand code is not tested for validity during data chain
ing.
Invalid Count: A ccw other than a ccw specifying
transfer in channel contains the value zero in bitpo sitions 48-63.
Invalid DataAddress: The channel has attempted
to transfer data to or from a location outside the main
storage of the particular installation. An invalid data
status indicates that no action has bcen taken at the
device in response to the command. If the condition
precluding normal execution of the operation occurs
after the execution has been started, unit exception is
accompanied by channel end, control unit end, or de
vice end, depending on when the condition was de
tected.
Termination of an operation with the unit-exception
indication causes command chaining to be suppressed.
the channel. Except for the conditions caused by equip
ment ma1functioning, they can occur only while the
subchannel is involved with the execution of an
Program-Controlled Interruption
The program-controlled-interruption condition is gen
erated when the channel fetches a ccw with the
ruption due to the
possible after fetching the ccw but may be delayed an
unpredictable amount of time because of masking of
the channel or other activity in the system.
Detection of the
progress of the
Incorrect Length
Incorrect length occurs when the number of bytes con
tained in the storage areas assigned for the
ation is not equal to the number of bytes requested or
offered by the
for one of the following reasons:
or sense operation, the device attempted to transfer
one or more bytes to storage after the assigned storage
areas were filled. The extra bytes have not been placed
operation the device requested one or more bytes from
the channel after the assigned main-storage areas were
exhausted. The count in the csw is zero.
ferred during a read, read hackward, or sense oper
ation is insufficient to fill the storage areas assigned to
the operation. The count in the csw is not zero.
write or control operation before all information
the device. The count in the csw is not zero.
The incorrect-length indication is suppressed when
112
the current ccw has the
operations and for operations rejected during the ini
tiation sequence.
Presence of the incorrect-length condition suppresses
command chaining unless the
or unless the condition occurs in an immediate oper
ation.
The following table lists the effect of the incorrect
length condition for all combinations of the
ations when the operation at the sub channel is termi
nated (stop) and when the command chaining takes
place. The entry
the indication is made available to the program; a
double hyphen (--) means that the indication is sup
pressed. For all entries, the current operation is as
sumed to have caused the incorrect-length condition.
FLAGS ACTION AND INDICATION
CD CC
1
I
I 1
I 1 1 Stop,IL Stop, --
Program Check
Program check occurs when programming errors are
detected hy the channel. The condition can be due to
the following causes:
Invalid C CW
transfer-in-channel command does not designate the
ccw on integral boundaries for double words. The
three low-order bits of the ccw address are not zero.
Invalid CCW
to fetch a ccw from a location outside the main stor
age of
has specified an invalid address in the
transfer-in-channel command or because on chaining
the channel has stepped the address above the highest
available location.
Invalid Command Code: The command code in the
first ccw designated by the
command chaining has four low-order zeros. The com
mand code is not tested for validity during data chain
ing.
Invalid Count: A ccw other than a ccw specifying
transfer in channel contains the value zero in bit
Invalid Data
to transfer data to or from a location outside the main
storage of the particular installation. An invalid data