function specified by the instruction
has been performed and, if not, the
reason for the rejection. In the case
of START I/O FAST RELEASE executed inde­
pendent of the device, a condition code
o may be set that is later superseded by
a deferred condition code stored in the CSW. The figure "Condition-Code Settings for I/O States and Functions" lists the I/O Conditions State SIO SIOF Available AAA O,1*a Interruption pending in device AAI 1*a Device working AAW 1*a Device not operational AAN 3a Interruption pending in subch. AIX
For the addressed device For another device 2
Subchannel working AWX
With the addressed device 2
With another device 2
Subchannel not operational ANX 3
Interruption pending in channel IXX aa Channel working WXX With the addressed device 2
With another device Internal activity Channel not operational NXX 3
Explanation:
I/O-system states and the corresponding
condition codes for each I/O function.
The I/O-system states and associated
abbreviations are defined in the section
"states of the Input/Output System"
earlier in this chapter. The digits in
the figure represent the decimal value
of the condition code. Condition-Code Settings TIO CLRIO HIO HDV RIO TCH STIDC CLRCH 0 0 1* 1* 0 0 0 0 1* 0 1* 1* 0 0 0 0 1* 0 1* 1* 0 0 0 0 3 0 3 3 0 0 0 0 1*" 1* 0 0 0 0 0 U 2 0 0 0 0 0 0 0 2 1* 1*" 1*" 0 0 0 0 2 0 1*" 0 0 0 0 0 3 3 3 3 0 0 0 0 0 1 n" 0 2 *** 2 + 0 2 "" 0& 2- ** 2 * 0 2 "" 0& 2- ** 2 * 0 2 "" 0& 3 3 3 3 3 3 3 3&& * Whenever condition code 1 is set, the CSW or its status portion is stored at
real location 64 during execution of the instruction. ** When CLEAR I/O encounters the WXX state, either condition code 2 is set, or
the channel is treated as available and the condition code is set according
to the state of the subchannel. When the channel is treated as available,
the condition codes for the WXX states are the same as for the AXX states. *** Condition code 1 (with the CSW stored) or 2 may be set, depending on the
channel. * The condition code depends on the state of the subchannel, the channel type,
and the system model. If the subchannel is not operational, condition code
2 or 3 is set. If the subchannel is available or working with the addressed
device, condition code 2 is set. Otherwise, condition code 0 or 2 is set. " When a "device not operational" response is received in selecting the ad­
dressed device, condition code 3 is set. "" When the channel is unable to store the channel ID because of the working or
interruption-pending state, a condition code 2 is set. If the working or
interruption-pending state does not preclude storing the channel 10, a con­
dition code 0 is set.
+ The condition code depends on the I/O interface sequence, the channel type,
and the system model. If the channel ascertains that the device received
the signal to terminate, a condition code 1 is set and the CSW stored. Otherwise, a condition code 2 is set. Condition-Code Settings for I/O States and Functions (Part 1 of 2) Chapter 13. Input/Output Operations 13-13

Explanation (Continued): • If the subchannel is interruption-pending for the addressed device, condi­
tion code 1 may be set depending on the channel type.
& On certain channels, when the working state precludes performing the 1/0- system reset, condition code 2 is set.
&& On certain channels, when the not-operational state is due to a channel­
check-stop condition, the instruction is executed, and condition code 0 is
set. Depending on the facilities provided for START I/O FAST RELEASE, some chan­
nels may set condition code O. If the subchannel is interruption-pending because of the concluding of the
portion of the operation involving the use of channel facilities, condition
code 2 is set. If the interruption-pending condition exists for other rea­ sons, condition code 1 is set. START I/O FAST RELEASE may cause the same condition code to be set as for
START I/O or may cause condition code 0 to be set. For the purpose of executing START I/O, START I/O FAST RELEASE, TEST I/O, CLEAR I/O, HALT DEVICE, and HALT I/O, a channel containing an interruption
condition appears the same as an available channel, and the condition code
setting depends on the states of the subchannel and device. The condition
codes for the IYY states are the same as for the AYY states, where the Ys represent the states of the subchannel and the device. As an example, the
condition code for the lAW state is the same as for AAW. Condition-Code Settings for I/O States and Functions (Part 2 of 2)
The channel-available state results in
condition code 0 only when no errors are
detected during the execution of the I/O instruction.
When a subchannel on a multiplexer chan­
nel contains an interruption condition
(state AIX), the I/O 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 oper­
ational, 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 detected to be
not operational.
Error conditions, including all equip­
ment or programming errors detected by
the channel or the I/O device during
execution of the I/O instruction, gener­
ally cause the CSW to be stored. Howev­
er, when the nature of the error causes
a machine-check interruption, but no I/O 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: 13-14 System/370 Principles of Operation
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 chan-
nel 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
its control equipment. (This
also true for STORE CHANNEL RESUME I/O, and TEST CHANNEL, RESUME I/O and TEST CHANNEL do
cause a CSW to be stored.)
in
i s
ID,
but
not
The channel may perform an I/O selective
reset or, on some models, may perform an
I/O-system 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:
can detect the following
errors during execution of
START I/O FAST RELEASE.
The channel
programming
START I/O or
All of the