Status When I/O Is
Idle
Attention c* Status modifier Control-unit end
Busy Channel end
Device end c* Unit check C Unit exception C Program-
controlled­
interruption
Incorrect length
Program check
Protection check Channel-data check
Channel-control C* check¢ Interface- C* control check Chaining check
Explanation:
After When or
Subch Upon Termination RIO or
Is of Operation at During Work i ng Command with Ctrl I/O Retry or
Device Subch Unit Dev Chaining C C C C C C C C C* C C C C C C* C C C C When SIO or When SIOF& Is TIO Is
Executed Executed S CS CS CS CS CS CS CS CS CS CS S CS CS CS S S CS S 5
S S S
S CS CS S When When When I/O ClRIO Is HIO or Inter­
Executed HDV Is ruption
S S 5
S S S
S
S
S
s
S
S CS CS S + Executed Occurs CS CS CS CS CS S S
S
S
S
S CS S
S S S S
S CS CS S C The channel or device can create or present status at the indicated time. A CSW or its status
portion is not necessarily stored at this time.
Status such as channel end or device end is created at the indicated time. Other status bits
may have been created previously but are made accessible to the program only at the indicated
time. Examples of such status bits are program check and channel-data check, which are detec­
ted while data is transferred but are made available to the program only with channel end, un­
less the PCI flag or an equipment malfunction has cause an interruption condition to be gen­
erated earlier. S The status indication is stored in the CSW at the indicated time.
An "S" appearing alone indicates that the status has been created previously. The letter "C" appearing with the "S" indicates that the status did not necessarily exist previously in the
form that causes the program to be alerted, and may have been created by the I/O instruction
or I/O interruption. For example, an equipment malfunction may be detected during an I/O in­
terruption, causing channel-control or interface-control check to be indicated; or a device
such as the IBM 3705 may signal temporary control unit busy in response to interrogation by an I/O instruction, causing status modifier, busy, and control-unit end to be indicated in the CSW. * The status generates an interruption condition. Channel end and device end do not result in interruption conditions when command chaining is
specified or command retry is signaled, and no other unusual situations have been detected.
Unit check does not result in an interruption condition when command retry is signaled and is
honored by the channel. Contents of the CSW Status Fields (Part 1 of 2) Chapter 13. Input/Output Operations 13-79

Explanation (Continued): This indication is created at the indicated time only by an immediate operation.
H When an operation on the selector channel has been concluded by HALT DEVICE or HALT I/O, or an
operation has been concluded by CLEAR I/O, channel end indicates the conclusion of the data­
handling portion of the operation at the control unit.
& When executed as SIO. When executed independent of the device.
+ The entries in this column apply only when the CLRIO function is executed. When CLEAR I/O causes the TIO function to be executed, the entries in the TIO column apply. Channel-control-check status may also be generated, and is then stored in the CSW, when the
STIDC function is executed. Contents of the CSW Status Fields (Part 2 of 2) CHANNEL LOGOUT When a channel stores a CSW that indi­
cates channel-control check in the
absence of logout pending, or
interface-control check, or, on some
channels, channel-data check, a channel
logout accompanies the storing of the CSW. Such a logout is useful for error
recovery. The logout may be a limited channel logout, a full channel logout,
or both. The type of logout that occurs
and, for the full channel logout, the
length of the full channel logout and
the location at which it is stored,
depend on the channel type and model.
The limited channel logout contains
model-independent information and is
stored at real locations 176-179 of the CPU to which the channel is connected.
When it is stored, bit 0 of the logout
is always stored as a zero.
The full channel logout contains model­
dependent information. When the length
of the full channel logout exceeds 96
bytes, it is stored at the location
specified by the I/O extended-logout (IOEL) address in real locations 173-175
of the CPU to which the channel is connected. When the length of the full
channel logout is 96 bytes or fewer, the
channel may either use the IOEL address
or store the full channel logout in the
fixed-logout area, real locations
256-351 of the CPU to which the channel
is connected. The information stored by
the STORE CHANNEL 10 instruction implies
whether the IOEL is used and, if it is
used, specifies the maximum full­
channel-logout length. The full­
channel-logout information may be stored in the IOEl area only when the IOEl-mask
bit (control register 14, bit 2) of the CPU to which the channel is connected is
one. I/O-COMMUNICATION AREA
Real locations 168-191 of the CPU to
which the channel is connected consti- 13-80 System/370 Principles of Operation
tute a permanently assigned area of
storage used by channels, designated the
I/O-communication area (IOCA). (See the
figure "I/O-Communication Area.")
Real location 172, 180-184, and 188-191
are reserved for future I/O use. Channel 10 (locations 168-171):
locations 168-171, when stored during the execution of a STORE CHANNEL 10 instruction, contain information which
describes the addressed channel. I/O Extended-logout Address (Locations 173-175): The I/O extended-logout (IOEl) address (real locations 173-175)
should be set by the program to desig­ nate an area in absolute storage to be
used by channels not capable of or not choosing to store the full chan­
nel logout in the fixed-logout area
(real locations 256-351). The rightmost
three bits of the I/O-extended-logout
address are reserved and are ignored by
the channel so that the full channel
logout always begins on a doubleword
boundary.
Whether the IOEl facility is used
depends on the channel type and model. Channels with a full-channel-Iogout
length not exceeding 96 bytes use either
the IOEl area or real locations 256-351
as the full-channel-logout area. Chan­ nels with a full-channel-logout length
exceeding 96 bytes use the IOEl area.
Programming Note
The extent of the full-channel-Iogout
area differs among channels and, for any
particular channel, may depend on the
features or engineering changes
installed. In order to provide for such
variations, the program should determine
the extent of the full channel logout by
means of STORE CHANNEL 10 whenever a
storage area for the full channel logout
is to be assigned.