stores logout information using the IOEl address, then this field is set to zero.
When the channel detects an equipment
malfunction during the execution of STORE CHANNEL 10, the channel causes the
status portion, bits 32-47, of the CSW to be replaced by a new set of status
bits. With the exception of the
channel-control-check bit (bit 45),
which is stored as a one, all bits in
the status field are stored as zeros.
The contents of the other fields of the CSW are not changed. When STORE CHANNEL 10 cannot be executed
because of a pending logout which
affects the operational capability of
the channel, a full CSW is stored. The
fields in the CSW are all set to zero,
with the exception of the logout-pending
bit and the channel-control-check bit,
which are set to ones. No channel
logout occurs in this case.
Program Exceptions:
Privileged operation
Resulting Condition Code: o Channel IO correctly stored
1 CSW stored
2 Channel activity prohibited
storing 10 3 Not operational
The condition code set by STORE CHANNEL IO for all possible states of the I/O system is shown in the figure "Condition Codes Set by STORE CHANNEL 10." See
"States of the Input/Output System" for
a detailed definition of the A, I, W, and N states. Channell: I : I ~ I : I A Available
I Interruption pending W Working
N Not operational • When the channel is unable to store
the channel IO because of its work­
ing state or because it contains a
pending interruption condition,
condition code 2 is set. If the
working or interruption-pending
state does not preclude the storing
of the channel 10, condition code 0 is set. Condition Codes Set by STORE CHANNEL ID
TEST CHANNEL TCH [S] '9FOO' o 16 20 31
The condition code in the PSW is set to
indicate the state of the addressed
channel. The state of the channel is
not affected, and no action is caused.
Bits 8-14 of the instruction are
ignored.
Bits 16-23 of the second-operand address
identify the channel to which the
instruction applies. Bit positions
24-31 of the address are ignored.
The TCH function is performed by the
TEST CHANNEL instruction and, on some
channels and under certain
circumstances, by CLEAR CHANNEL. The TCH function inspects only the state
of the addressed channel. It tests
whether the channel is operating in the
burst mode, is interruption-pending, or
is not operational. When the channel is
operating in the burst mode and contains
an interruption condition, the condition
code is set as for operation in the
burst mode. When none of these situ­
ations exist, the available state is
indicated. No device is selected, and, on the multiplexer channel, the subchan­
nels are not interrogated.
Program Exceptions:
Privileged operation
Resulting Condition Code: o Channel available
1 Interruption or logout condi­
tion 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 "Condi­ tion 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. Channell~ ---:--~---~--~I-:~I--:~I A Available
I Interruption pending W Working N Not operational
Condition Codes Set by TEST CHANNEL Chapter 13. Input/Output Operations 13-33

TEST I/O TIO [S] '9DOO' 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, subchannel, and I/O device to which the instruction
applies.
The TIO function is performed by the
instruction TEST I/O and, on some chan­
nels and under certain circumstances, by CLEAR I/O. When the channel is operating in burst
mode and the addressed subchannel
contains an interruption condition for
the addressed device, 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 to identify the interruption
condition, and the interruption condi­
tion is cleared. 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 status causing the inter­
ruption condition from the device. Condition code 2 is set in this case.
When the channel is either available or
interruption-pending and the addressed
subchannel is either interruption­
pending for a different device or work­
ing, the TIO function causes condition
code 2 to be set.
When either of the situations described
in the following two paragraphs occurs
with the channel either available or
interruption-pending or, on some chan­
nels, working, 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 interruption­
pending for the addressed device,
and the interruption condition is
due to the termination of an I/O operation at the subchannel. When
the CSW is stored, the interruption
condition is cleared. The CSW fields contain the final values for
the I/O operation. The unit-status
and/or channel-status fields
contain indications provided by the
device or channel respectiVely,
which identify the interruption
13-34 System/370 Principles of Operation
condition and any other conditions
detected by the channel or device.
2. The subchannel is interruption-
pending for the addressed device,
and the interruption condition is
not due to the termination of an I/O operation at the sUbchannel.
When the CSW is stored, the inter­
ruption condition is cleared. The
subchannel key, CCW address, and
count fields are stored as zeros.
The unit-status field contains
indications provided by the device
which identify the interruption
condition. The channel-status
field contains zeros unless a chan­
nel equipment error is detected.
When any of the following situations
occurs with the channel either available
or interruption-pending, the TIO func­
tion causes the CSW to be stored. The
contents of the entire CSW pertain to
the I/O device addressed by the instruc­
tion.
1. The subchannel is available, and
the I/O device contains an inter­
ruption 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 inter­
ruption 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 associ­
ated 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 equip­
ment 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 subchannel.
When the TIO function cannot be executed
because of a pending logout which
affects the operational capability of
the channel or subchannel, a full CSW is
stored. The fields in the CSW are all
set to zeros, with the exception of the