Channel ID I IOEl Address 168 172
176 180 184 188 limited Channel logout IMeasurement By tel I/O-Communication Area
limited Channel logout (locations
176-179): The limited-channel-logout (lCl) field (real locations 176-179)
contains model-independent information
related to equipment errors detected by
the channel. This information is used
to provide detailed machine status when
errors have affected I/O operations.
The field may be stored only when the CSW or a portion of the CSW is stored.
The limited-channel-logout facility may
not be available on all channels. The
field, if stored, mayor may not be
accompanied by the full channel logout. Channels which do not store the
limited-channel-logout field usually
store equivalent information in the full
channel logout.
The bits of the field are defined as
follows:
o
1-3
This bit is always stored as a
zero when a limited channel
logout is stored. If the
program ensures that this bit is
set to one and any channel­
control check, interface-control
check, or channel-data check
occurs, a test of this bit can
determine if the limited channel
logout was stored by the
channel. The limited channel
logout cannot be stored by a
channel unless one of these
three channel-status bits is set
to one.
Identity of the storage-control
unit (SCU). This identifies the SCU through which storage refer­
ences were directed when an
error was detected. This iden­
tity is not necessarily the
identity of the storage unit
involved with data transfer. When only one physical path
exists between channel and stor­
age, the storage-control unit
has the identity of the CPU to
which the channel is connected.
If more than one path exists,
the storage-control unit has its
own identity. I/O Address
4-7
8-12
When bit 3 is zero, bits 1 and 2
are undefined. In this case,
the SCU identity is implied to
be the same as the identity of
the CPU to which the channel is
connected. When bit 3 is one,
the binary value of bits 1 and 2
identifies a physical SCU. Each SCU in the system has a unique
identity.
Detect field. This identifies
the that detected
the error. At least one bit is present in this field, and
multiple bits may be set when
more than one unit detects the
error.
Bit 4
Bit 5
Bit 6
Bit 7 CPU Channel Main-storage control
Main storage Source field. This indicates
the most likely source of the
error. The determination is
made by the channel on the basis
of the type of error check, the
location of the checking
station, the information flow
path, and the success or failure
of transmission through previous
check stations.
Normally, only one bit will be
present in this field. However,
when interunit communication
cannot be resolved to a 3ingle
unit, such as when the interface
between units is at fault,
multiple bits (normally two) may
be set to ones in this field.
When a reasonable determination
cannot be made, all bits in this
field are set to zeros.
If the detect and source fields
indicate different units, the
interface between them can also
be considered suspect.
Bit 8 -- CPU Bit 9 -- Channel Bit 10 Main-storage control
Bit 11 Main storage
Bit 12 -- Control unit Chapter 13. Input/Output Operations 13-81

13-14
15-23
24-25
26
27
Reserved. Stored zero. Field-validity These
bits indicate the validity of
the information stored in the designated fields. When the validity bit is set to one, the
field is stored and usable.
When the validity bit is set to zero, the field is not usable.
The fields designated are: Bit 15 --Full channel logout.
Bit 16
Bit 17
Bit 18
Bit 19
Bit 20 Bit 21
Bit 22
Bit 23
This bit is set to
one, by models that
implement the recovery-extension
facility, when full­
channel-logout in­
formation with correct
contents is stored by
the channel. Other­ wise, the bit is
stored as zero. Reserved. Stored zero
Reserved. Stored zero
Reserved. Stored zero
Sequence code
Unit status
CCW address and sub­
channel key in CSW
Channel address
Device address of termination that has
occurred is indicated by these
two bits.
This encoded field has meaning
only when a channel-control
check or an interface-control
check is indicated in the CSW.
When neither of these two checks
is indicated, no termination has
been forced by the channel. 00 Interface disconnect 01 Stop, stack, or normal
termination 10 Selective reset
11 reset
Reserved. Stored zero.
Interface inoperative. When the
recovery-extension facility is
installed, this bit is set to
one when the channel detects an I/O-interface malfunction which
persists after selective reset
is signaled on the interface.
Interface-control check,
channel-control check, or both
are also set when this condition
is detected. When the
recovery-extension facility is
not installed, bit 27 is stored
as zero.
Programming note: This bit
implies that devices involved in
active I/O operations related to
13-82 System/370 Principles of Operation 28
29-31
the identified channel may have
been left in the working state. CLEAR CHANNEL addressed to that
channel can be used to relieve
the condition. I/O-error alert. This bit, when
set to one, indicates that the
limited channel logout resulted
from the signaling of I/O-error alert by the indicated unit.
The I/O-error-alert signal indi­
cates that the control unit has
detected a malfunction which
prevents it from communicating
properly with the channel. The
channel, in response, performs
an I/O selective reset and caus­ es interface-control check to be
set.
Seguence code. This code iden­
tifies the I/O sequence in
progress at the time of error.
It is meaningless if stored
during the execution of HALT I/O or HALT DEVICE. For all cases, the CCW address
in the CSW, if validly stored
and nonzero, is the address of
the current CCW plus 8.
The sequence code assignments
are: 000 A channel-detected error
occurred during the
execution of a TEST I/O or CLEAR I/O instruction. 001 A nonzero command byte has
been sent by the channel,
but device status has not
yet been analyzed by the
channel. This code is set
during initial selection. 010 The command has been
accepted by the device, but
no data has been
transferred. This code is
set if the initial status is either channel end alone, or
channel end and device end,
or channel end, device end,
and status modifier, or all
zeros.
all At least one byte of data
has been transferred between the channel and the device. This code is also used when the channel is in an idle or
polling state. 100 The command in the current CCW has either not yet been sent to the device or else was sent but not accepted by the device. This code is
set when one of the follow­
ing situations occurs: