nel fails to accept a byte on an input operation, the
following data in main storage are shifted to fill the
gap.On an output operation, overrun indicates that
data recorded at the device may be invalid. The over
run bit is also turned on when the device receives the
new command too late during command chaining.
All information significant to the use of the device
normally is provided in the first two bytes. Any bit
positions following those used for programming in
formation contain diagnostic information, which may
extend to as many bytes as needed. The amount and
the meaning of the status information are peculiar to
the type ofI/O device and are specified in the SRL publication for the device.
The sense information pertaining to the lastI/O op
eration is reset by the next command, other than
sense, addressed to the control unit. The sense com
mand cannot cause the command-reject, intervention
required, data-check, or overrun bits to be turned on.
If the control unit detects an equipment error or in
valid parity of the sense command code, the equip
ment-check or bus-out-check bits are turned on, and
unit check is sent with the channel end.
A ccw used in a sense operation is inspected for
everyone of the five flags -CD, CC,SLI, skip, and PCI. Bit positions 0-3 of the ccw contain modifier bits.
TransferIn Channel
The next ccw is fetched from the location designated
by the data-address field of the ccw specifying trans-
fer in channel. The transfer-in-channel command does
not initiate anyI/O operation at the channel, and the I/O device is not signaled of the execution of the com
mand. The purpose of the transfer in channel com
mand is to provide chaining between ccw's not lo
cated in adjacent double-word locations in an ascend
ing order of addresses. The command can occur in
both data and command chaining.
The first ccw designated by the CAW may not specify
transfer in channel. When this restriction is violated,
noI/O operation is initiated, and the program-check
condition is generated. The error causes the status por
tion of the csw with the program-check indication to
be stored during the execution ofSTART I/O. To address a ccw on integral boundaries for double
words, a ccw specifying transfer in channel must con
tain zeros in bit positions 29-31. Furthermore, a ccw
specifying a transfer in channel may not be fetched
from a location designated by an immediately preced
ing transfer in channel. When either of these errors is
detected or when an invalid address is specified in
transfer in channel, the program-check condition is
generated. Detection of these errors during data chain
ing causes the operation at theI/O device to be ter
minated, whereas during command chaining they
cause an interruption condition to be generated.
The contents of the second half of the ccw, bit po
sitions 32-63, are ignored. Similarly, the contents of bit
positions0-3 of the ccw are ignored.
Input/OutputOperations 103
following data in main storage are shifted to fill the
gap.
data recorded at the device may be invalid. The over
run bit is also turned on when the device receives the
new command too late during command chaining.
All information significant to the use of the device
normally is provided in the first two bytes. Any bit
positions following those used for programming in
formation contain diagnostic information, which may
extend to as many bytes as needed. The amount and
the meaning of the status information are peculiar to
the type of
The sense information pertaining to the last
eration is reset by the next command, other than
sense, addressed to the control unit. The sense com
mand cannot cause the command-reject, intervention
required, data-check, or overrun bits to be turned on.
If the control unit detects an equipment error or in
valid parity of the sense command code, the equip
ment-check or bus-out-check bits are turned on, and
unit check is sent with the channel end.
A ccw used in a sense operation is inspected for
everyone of the five flags -CD, CC,
Transfer
The next ccw is fetched from the location designated
by the data-address field of the ccw specifying trans-
fer in channel. The transfer-in-channel command does
not initiate any
mand. The purpose of the transfer in channel com
mand is to provide chaining between ccw's not lo
cated in adjacent double-word locations in an ascend
ing order of addresses. The command can occur in
both data and command chaining.
The first ccw designated by the CAW may not specify
transfer in channel. When this restriction is violated,
no
condition is generated. The error causes the status por
tion of the csw with the program-check indication to
be stored during the execution of
words, a ccw specifying transfer in channel must con
tain zeros in bit positions 29-31. Furthermore, a ccw
specifying a transfer in channel may not be fetched
from a location designated by an immediately preced
ing transfer in channel. When either of these errors is
detected or when an invalid address is specified in
transfer in channel, the program-check condition is
generated. Detection of these errors during data chain
ing causes the operation at the
minated, whereas during command chaining they
cause an interruption condition to be generated.
The contents of the second half of the ccw, bit po
sitions 32-63, are ignored. Similarly, the contents of bit
positions
Input/Output