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Program Exceptions:
Privileged Operation
Resulting Condition Code:
o
Subchannel busy with another device or
interruption pending
1
CSW stored
2
Channel working
3
Not operational
The condition code set by HALT DEVICE for
all possible states of the I/O system is shown in the
figure" Condition Codes Set by HALT DEVICE."
See the section "States of the Input/ Output
System" in this chapter for a detailed definition of
the A, I, W, and N states.
Programming Note
The execution of HALT DEVICE always causes
data transfer between the addressed device and the
channel to be terminated. The condition code and
the CSW (when stored) indicate whether the
control unit was signaled to terminate its operation
during the execution of the instruction. If the
control unit was not signaled to terminate its
Channel
A
Subchannel
A
Control Unit
- Device
1*
A
I
W
Available
Interruption pending
Working
A
wit
W#
N
o
0
3
A
operation, the condition code and the CSW (when
stored) imply the situations under which the
execution of a HALT DEVICE for the same
address will cause the control unit to be signaled to
terminate.
Condition Code 0 indicates that HALT DEVICE
cannot signal the control unit until an interruption
condition on the same subchannel is cleared.
Condition Code 1 with Control-Unit-Busy Status
in the CSW indicates that HALT DEVICE cannot
signal the coritrol unit until the control-unit-end
status is received from that control unit.
Condition Code 1 with Zeros in the Status Field
of the CSW indicates that the addressed device
was selected and signaled to terminate the current
operation, if any.
Condition Code 2 indicates that the control unit
cannot be signaled until the channel is not working.
The end of the working state can be detected by
noting an interruption from the channel or by
noting the results of repeatedly executing HALT
DEVICE.
Condition Code 3 indicates that manual
intervention is required in order to allow HALT
DEVICE to signal the control unit to terminate.
w#
N
o
0
•
N
3
Wit
=
Working with a device other than the one addressed
W#
=
Working with the addressed device
N
*
@
+
•
Not operational
CSW Stored
In the W#XX state, either condition code 1 (with CSW stored) or condition code 2
may be set, depending on the channel. However, condition code 1 (with CSW stored)
can be set only if the control unit has received the signal to terminate or if
control-unit-busy status is received by the channel.
In the WitlX and WitWitX states, either condition code 0 or 2 may be set.
In the WitNX state, either condition code 2 or 3 may be set, depending. on the model
and the channel type.
Note: Underscored condition codes pertain to situations that can occur only on the
multiplexer channel.
Condition Codes Set
by
HALT DEVICE
12-18
IBM 4300 Processors Principles of Operation
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