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13-18
19-23
24-25
26-27
28
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
single 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 II-Main storage
Bit 12-Control unit
Reserved. Stored zero.
Field-validity flags.
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 19-5equence code
Bit 20-Unit status
Bit 21-CCW address and key in CSW
Bit 22-Channel address
Bit 23-Device address
Type 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 Reserved
Reserved. Stored zero.
I
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.
29-31
The I/O-error-alert signal indicates that
the control unit has detected a
malfunction which prevents it from
communicating properly with the
channel. The channel, in response,
performs a malfunction reset and causes
interface-control check to be set.
Sequence code identifies the 1/0
sequence in progress at the time of
error.
It
is meaningless if stored during
the execution of HALT 110 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
110 or CLEAR 110 instruction.
001 Command-out with a nonzero
command byte on bus-out has been
sent by the channel, but device
status has not yet been analyzed by
the channel. This code is set with
a command-out response to
address-in during initial selection.
010 The command has been accepted
by the device, but no data has been
transferred. This code is set by a
service-out or command-out
response to status-in during an
initial selection sequence, if the
status is either channel end alone,
or channel end and device end, or
channel end, device end, and status
modifier, or all zeros.
011 At least one byte of data has been
transferred between the channel
and the device. This code is set
with a service-out response to
service-in and, when appropriate,
may be 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 following
situations occurs:
1. When the CCW address is
updated during command
chaining or a START 1/0.
2. When service-out or
command-out is raised in
Chapter 12. Input/Output Operations
12-61
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