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Bit
Position Function
1, 2
3
4
5,6
Devi ce condition: if bits 1 and 2 are 00 (device
"ready II), all devi ce conditions required for proper
operation are satisfied.
If bits 1 and 2 are 01
(devi ce "not operational II), the addressed device
has developed some condition that will not allow
it to proceed; in either case, operator intervention
is usually required. If bits 1 and 2 are 10 (device
IIUnavailable ll ), the device has more than one
channel of communication avai lable and it is en-
gaged in an operation controlled by a controller
other than the one specified by the I/O address.
If bits 1 and 2 are 11 (device IIbusyll), the device
has accepted a previous SIO instruction and is al-
ready engaged in an I/O operation.
Device mode: if this bit is 1, the device is in the
lIautomatic ll mode; if this bit is 0, the device is
in the IImanual
li
mode and requires operator inter-
vention. This bit can be used in conjunction with
bits 1 and 2 to determine the type of action re-
qu ired.
For exam pi e, assume that a card reader
is abl e to operate, but no cards are in the hopper.
The card reader wvuld be in state 000 (device
IIreadyll, but manual intervention required), where
the state is indicated by bits 1, 2, and 3 of the
I/o
status response. If the operator subsequently
loads the card hopper and presses the card reader
START switch, the reader would advance to state
001 (device IIreadyll and in automatic operation).
If the card reader is instate 000 when an SIO i n-
struction is executed, the SIO would be accepted
by the reader and the reader would advance to
state 110 (device IIbusyll, but operator intervention
required).
Should the operator then place cards
in the hopper and press the START switch, the card
reader state would advance to 111 (device IIbusy"
and in automatic operation), and the input opera-
tion would proceed. Should the card reader sub-
sequently become empty (or the operator press the
STOP switch) and command chaining is being used
to read a number of cards, the card reader would
return to state 110. If the card reader is instate
001 when an SIO instruction is executed, the
reader advances to state 111, and the input'opera-
tion continues as normal.
Should the hopper sub-
sequently become empty (or should the operator
press the card reader STOP switch) and command
chaining is being used to read a number of cards,
the reader would go to state 110 unti
I
the operator
corrected the situation.
Unusual end: if this bit is 1, the previous I/O op-
eration terminated in an
II
unusual end ll condition.
These conditions vary from device to device (see
the applicable peripheral reference manual).
Device controller condition:
if
bits 5and 6 are 00
(device controller "readyll), all device controller
conditions required for its proper operation are
satisfied. If bits 5 and 6 are 01 (device controller
Bit
Position Function
5,6
(cont.)
7
8
9
10
11
II not operational"), some condition has developed
that does not allow it to operate properly.
In
either case, operator i nterventi on is usually re-
qui red. If bits 5 and 6 are 10 (device controller
"unavailable"), the device controller is currently
engaged in an operation controlled by an lOP
other than the one addressed by the I/O instruction.
If bits 5 and 6 are 11 (device controller "busy"),
the device controller has accepted a previ ous
SIO instruction and is currently engaged in per-
forming an operati on for the addressed lOP.
Reserved
Incorrect length: if this bit is 1, an incorrect
length condition has been detected during the
previous operation. Incorrect length is caused
by a channel end (or end of record) condition
occurring before the device controller has re-
ceived a IIcount done" signal from the lOP, or is
caused by the de vi ce controller recei vi ng a count
done signal before channel end (or end of record);
e. g., count done before 80 columns have been
read from a card. Normally, a count done signal
is sent to the device controller by the lOP to in-
dicate that the byte count associated with the
current operati on has been reduced to zero.
The
lOP is capable of suppressing an error condition on
incorrect length, since there are many situations
in which incorrect le.ngth is a legitimate situation
and not a true error condition. Incorrect length is
suppressed as an error by coding the SIL flag (a 1
in bit 38) of the lOP command doubleword (see
IIFlags ll , Chapter 4). At the end of the execution
of an I/O command list, this status bit is 1 if an
incorrect length condition occurred anywhere in
the command list, regardless of the coding of the
SIL flag.
Transmission data error: this bit is set to 1 if the
lOP or device controller has detected a parity
error or data overrun in the transmitted informa-
tion. At the end of an execution of an I/O com-
mand list, this status bit is 1 if a transmission data
error occurred anywhere in the command list.
Transmission memory error: this bit is set to 1 if
a memory parity error has occurred during a data
input/output operation. A parity error is detected
on any output operation and on partial-word input
operations. At the end of an execution of an I/O
command list, this status bit is 1 if a transmission
memory error occurred anywhere in the command
list. A device halt occurs only if the HTE flag
in the lOP command doubleword is set to 1 (see
II
Flags ll , Chapter 4).
Memory address error: a nonexi stent memory address
has been encountered on ei ther data or commands.
Operation is terminated with an
II
unusual end".
Input/Output Instructions
85
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