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The available state results in condition code 0
only when no errors are detected during the
execution of the 1/
°
instruction.
When a sub channel on a multiplexer channel
contains an interruption condition (state AIX), the
1/
°
device associated with the concluded operation
normally is in the interruption-pending state.
When the channel detects during the execution of
TEST I/O that the device is not operational,
condition code 3 is set. Similarly, condition code 3
is set when HALT I/O or HALT DEVICE is
addressed to a subchannel in the working state
(state AWX), but the device is not operational.
Error conditions, including all equipment or
programming errors detected by the channel or the
1/
°
device during execution of the I/O instruction,
generally cause the CSW to be stored. However,
when the nature of the error causes a
machine-check interruption, but no 1/
°
interruption, to occur, the CSW is not stored.
Three types of errors can occur:
Channel-Equipment Error: The channel can detect
the following equipment errors during execution of
START I/O, START I/O FAST RELEASE, TEST
I/O, CLEAR I/O, HALT I/O, and HALT
DEVICE:
1.
The channel received an address from the
device during initial selection that either had a
parity error or was not the same as the one the
channel sent out. Some device other than the
one addressed may be malfunctioning.
2. The unit-status byte that the channel received
during initial selection had a parity error.
3. A signal from the I/O device occurred at an
invalid time or had invalid duration.
4. The channel detected an error in its control
equipment. (This is also true for STORE
CHANNEL ID and TEST CHANNEL.)
The channel may perform an I/O selective reset
or generate a halt signal, depending on the type of
error and the model. If a CSW is stored,
channel-control check or interface-control check is
indicated, depending on the type of error.
Channel-Programming Error: The channel can
detect the following programming errors during
execution of START 1/
°
or START 1/
°
FAST
RELEASE. All of the errors are indicated during
START I/O, and during START I/O FAST
RELEASE when it is executed as START I/O, by
the condition-code setting and by the status portion
of the CSW. When the SIOF function is
performed, the first two errors are indicated as for
START I/O, and the remaining errors are indicated
in a subsequent interruption.
1. Invalid CCW -address specification in CAW
2. Invalid CAW format
3. Storage location of first CCW not provided
4. First-CCW location in a disconnected page
5. First-CCW location protected against fetching
6. First CCW specifies transfer in channel
7. Invalid command code in first CCW
8. Invalid count in first CCW
9. Invalid format for first CCW
The CSW indicates program check, except for
items 4 and 5, for which protection check is
indicated.
Device Error: Programming or equipment errors
detected by the device during the execution of
START I/O, or START I/O FAST RELEASE are
indicated by unit check or unit exception in the
CSW.
The causes of unit check and unit exception for
each type of 1/
°
device are detailed in the SL
publication for the device.
Instruction Formats
All I/O instructions use the following S format:
Op
Code
o
16
20
31
Except for STORE CHANNEL ID, bit positions
8-14 of these instructions are ignored. Bit position
15 is ignored by the instruction TEST CHANNEL
but is decoded as· part of the operation code for
CLEAR I/O, HALT DEVICE, HALT I/O,
START I/O, START I/O FAST RELEASE, and
TEST I/O.
The second -operand address specified by the B2
and D2 fields is not used to designate data but
instead is used to identify the channel and I/O
device. Address computation follows the rules of
address arithmetic. The address has the following
format:
1IIIIIIIIIchn
AddrlDev Addrl
8
16
24
31
Bit positions 16-31 contain the 16-bit I/O
address. Bit positions 8-15 are ignored.
Chapter 12. Input/Output Operations
12-13
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