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state is indicated. No device is selected, and, on
the multiplexer channel, the subchannels are not
interrogated.
Program Exceptions:
Privileged Operation
Resulting Condition Code:
o
Channel available
1
Interruption or logout condition in channel
2
Channel operating in burst mode
3
Channel not operational
The condition code set by TEST CHANNEL for
all possible states of the addressed channel is
shown in the figure "Condition Codes Set by TEST
CHANNEL." See the section "States of the
Input/ Output System" in this chapter for a detailed
definition of the A, I, W, and N states.
Channe 1
11---:--+-----+1-:--+1-: -I I
A
Available
I
Interruption pending
W
Working
N
Not operational
Condition Codes Set
by
TEST CHANNEL
rEST I/O
TID
[5]
9000
o
16
20
31
The state of the addressed channel, subchannel,
and device is indicated by setting the condition
code in the PSW and, in certain situatIOns, by
storing the CSW. Interruption conditions may be
cleared. Bits 8-14 of the instruction are ignored.
Bits 16-31 of the second-operand address
identify the channel, sub channel, and I/O device to
which the instruction applies.
The TIO function is performed by the instruction
TEST I/O and, under certain circumstances, by
CLEAR I/O.
When the channel is operating in burst mode and
the addressed subchannel contains an interruption
condition, the TIO function causes condition code
1 or 2 to be set, depending on the model and
channel type. If condition code 1 is set, the CSW
is stored at location 64 to identify the interruption
condition, and the interruption condition is cleared.
When the situation described in the following
paragraph occurs with the channel either available
or interruption-pending or, on some channels,
working, the TIO function causes theCSW to be
stored. The contents of the entire CSW pertain to
the I/O device addressed by the instruction.
The sub channel contains an interruption
condition due to a terminated operation at the
addressed device. The CSW identifies the
interruption condition, and the interruption
condition is cleared. The subchannel key,
CCW address, and count fields contain the
final values for the I/O operation, and the
status field may include bits provided by the
channel and the device. The interruption
condition in the subchannel is not cleared, and
the CSW is not stored if the channel is working.
and has not yet accepted the interruption
condition from the device.
When any of the following situations occurs with
the channel either available or interruption-
pending, the TIO function causes the CSW to be
stored. The contents of the entire CSW pertain to
the I/O device addressed by the instruction.
1. The subchannel is available, and the I/O device
contains an interruption condition or the
control unit contains control-unit end for the
addressed device. The CSW unit-status field
identifies the interruption condition and may
contain other bits provided by the device or
control unit. The interruption condition is
cleared. The busy bit in the CSW is zero. The
other fields of the CSW contain zeros unless an
equipment error is detected.
2. The subchannel is available, and the I/O device
or the control unit is executing a previously
initiated operation or the control unit has an
interruption condition associated with a device
other than the one addressed. The CSW
unit-status field contains one in the busy-bit
position or, if the control unit is busy, the busy
and status-modifier bits are ones. Other fields
of the CSW contain zeros unless an equipment
error is detected.
3. The subchannel is available, and the I/O device
or channel detected an equipment error during
execution of the instruction or the addressed
device is not ready and does not have any
interruption condition. The CSW identifies the
error. If the device is not ready, unit check is
indicated. No interruption conditions are
generated at the I/O device or the sub channel.
Chapter 12. Input/Output Operations
12-25
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