The fields in the csw are allocated for the following
purposes:Protection Key: Bits 0-3 form the storage protection
key used in the chain of operations initiated by the
lastSTART I/O. Command Address: Bits 8-31 form an address that
is eight higher than the address of the last ccw used.
Status: Bits 32-47 identify the conditions in the de
vice and the channel that caused the storing of the
csw. Bits 32-39 are obtained over theI/O interface and
indicate conditions detected by the device or the con
trol unit. Bits40-47 are provided by the channel and
indicate conditions associated with the subchannel.
Each of the 16 bits represents one type of condition,
as follows:nIT DESIGNATION BIT DESIGNATION
32 Attention40 Pro gram -con trolled
interruption
33 Status modifier 41 Incorrcct length
34Control unit end 42 Program check
35 Busy 43 Protection check
36Channel end 44 Channel data check
37 Device end 45Channel control check
38 Unit cheek 46 Interface control check
39 Unit exception 47 Chaining check
Count: Bits 48-63 form the residual count for the
last ccw used.
Unit StatusConditions The following conditions are detected by the I/O de
vice or control unit and are indicated to the channel
over theI/O interface. The timing and causes of these
conditions for each type of device are specified in theSRL publication for the device.
When theI/O device is accessible from more than
one subchannel, status is signaled to the sub channel
that initiated the associatedI/O operation. The han
dling of conditions not associated withI/O operations
depends on the type of device and condition and is
specified in theSRL publication for the device.
The channel does not modify the status bits received
from theI/O device. These bits appear in the csw as
received over the interface.
Attention
Attention is caused upon the generation of the atten
tion signal at theI/O device. The attention signal can
be generated at any time and is interpreted by the
program. Attention is not associated with the initiation,
execution, or termination of anyI/O operation.
The attention condition cannot be indicated to the
program while an operation is in progress at theI/O device, control unit, or subchannel. Otherwise, the
handling and presentation of the condition to the chan
nel depend on the type of device.
StatusModifier Status modifier is generated by the device when the
normal sequence of commands has to be modified or
when the control unit detects during the selection
sequence that it cannot execute the command or in
struction as specified.
When the status-modifier condition is provided in
response toTEST I/O, presence of the bit indicates that
the device cannot execute the instruction and that no
bits pertaining to the current status of the device have
been provided. The status of the device and subchan
nel is not changed, and the csw stored byTEST I/O contains zeros in the key, command address, channel
status, and count fields. The2702 Transmission Con trol is an example of a type of device that cannot
executeTEST I/O. When the status-modifier bit appears in the csw to
gether with the busy bit, it indicates that the busy
condition pertains to the control unit associated with
the addressedI/O device. The control unit appears
busy when it is executing a type of operation or is in
a state that precludes the acceptance of any command
or the instructionTEST I/O and HALT I/O. This occurs
for operations such as backspace tapefile, in which
case the control unit remains busy after providing
channel end, and for operations terminated on the
selector channel by HALTI/O. The combination of
busy and status modifier can be provided in response
to any command as well asTEST I/O and HALT I/O. Presence of both busy and status modifier in response
toTEST I/O is handled the same way as when status
modifier alone is on.Once the execution of a command has been initi
ated, the status-modifier indication can be provided
only together with device end. The handling of this
set of bits by the channel depends on the operation.
If command chaining is specified in the current ccw
and no unusual conditions have been detected, pres
ence of the bit causes the channel to fetch and chain
to the ccw whose main-storage address is 16 higher
than that of the current ccw. If theI/O device signals
the status-modifier condition at a time when the chain
command flag is off or when any unusual conditions
have been detected, no action is taken in the channel,
and the status-modifier bit is placed in the csw.
Programming Note
When the multiplexor channel detects a programming
error during command chaining, the interruption con
dition is queued at theI/O device. On devices such as
the2702 Transmission Control, queuing of the con
dition may generate the status-modifier indication,
which subsequently appears in the csw associated
with the termination of the operation.Input/Output Operations 109
purposes:
key used in the chain of operations initiated by the
last
is eight higher than the address of the last ccw used.
Status: Bits 32-47 identify the conditions in the de
vice and the channel that caused the storing of the
csw. Bits 32-39 are obtained over the
indicate conditions detected by the device or the con
trol unit. Bits
indicate conditions associated with the subchannel.
Each of the 16 bits represents one type of condition,
as follows:
32 Attention
interruption
33 Status modifier 41 Incorrcct length
34
35 Busy 43 Protection check
36
37 Device end 45
38 Unit cheek 46 Interface control check
39 Unit exception 47 Chaining check
Count: Bits 48-63 form the residual count for the
last ccw used.
Unit Status
vice or control unit and are indicated to the channel
over the
conditions for each type of device are specified in the
When the
one subchannel, status is signaled to the sub channel
that initiated the associated
dling of conditions not associated with
depends on the type of device and condition and is
specified in the
The channel does not modify the status bits received
from the
received over the interface.
Attention
Attention is caused upon the generation of the atten
tion signal at the
be generated at any time and is interpreted by the
program. Attention is not associated with the initiation,
execution, or termination of any
The attention condition cannot be indicated to the
program while an operation is in progress at the
handling and presentation of the condition to the chan
nel depend on the type of device.
Status
normal sequence of commands has to be modified or
when the control unit detects during the selection
sequence that it cannot execute the command or in
struction as specified.
When the status-modifier condition is provided in
response to
the device cannot execute the instruction and that no
bits pertaining to the current status of the device have
been provided. The status of the device and subchan
nel is not changed, and the csw stored by
status, and count fields. The
execute
gether with the busy bit, it indicates that the busy
condition pertains to the control unit associated with
the addressed
busy when it is executing a type of operation or is in
a state that precludes the acceptance of any command
or the instruction
for operations such as backspace tape
case the control unit remains busy after providing
channel end, and for operations terminated on the
selector channel by HALT
busy and status modifier can be provided in response
to any command as well as
to
modifier alone is on.
ated, the status-modifier indication can be provided
only together with device end. The handling of this
set of bits by the channel depends on the operation.
If command chaining is specified in the current ccw
and no unusual conditions have been detected, pres
ence of the bit causes the channel to fetch and chain
to the ccw whose main-storage address is 16 higher
than that of the current ccw. If the
the status-modifier condition at a time when the chain
command flag is off or when any unusual conditions
have been detected, no action is taken in the channel,
and the status-modifier bit is placed in the csw.
Programming Note
When the multiplexor channel detects a programming
error during command chaining, the interruption con
dition is queued at the
the
dition may generate the status-modifier indication,
which subsequently appears in the csw associated
with the termination of the operation.