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Sense Byte; Interface Stop Signal; Halt; Commands - IBM 2702 Information Manual

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Channel End and Device End.
This status-byte con-
figuration indicates to the channel that the command
was executed successfully. No errors or unusual
conditions were detected during the execution of the
command.
Channel End, Device End, and Status Modifier. This
configuration indicates a positive response to a Poll
from a start/stop or Binary-Synchronous terminal.
This status can also signal that a SYN character was
not received within three seconds after the ENQ char-
acter was transmitted on a BSC Poll command.
For an Adprep command this status configuration
signals that the 2703's poll address was received.
Channel End, Device End, and Unit Exception. This
status-byte configuration indicates to the channel
that some unusual condition was detected during the
execution of the current command. The type of
condition indicated will depend on the command just
executed and the terminal type being operated on.
Channel End, Device End, and Unit Check. This
status-byte configuration indicates to the channel
that some error condition was detected during the
execution of the current command. Since a large
number of error conditions may arise, a Sense
command must be iss\led to this communications
line to further identify the error.
Channel End, Device End, Unit Exception, and Unit
Check. The conditions that cause this status to be
signaled are a combination of the conditions that
would cause Channel End, Device End, and Unit
Exception status plus some error condition(s). As
in "Channel End, Device End, and Unit Check, " a
Sense command must be issued to further identify
the error conditions. The Unit Exception bit will be
generated from the same conditions as described in
"Channel End, Device End, and Unit Exception. "
Sense Byte
The sense byte is transferred to the multiplexer
channel only when a Sense command is issued. The
various bit positions within the byte are set by differ-
ent sense conditions, as indicated in Figures 2-11
through 2-18.
The sense information pertaining to the previous
I/O operation is reset by the next command addressed
to a line (except for I/o No-Op, Halt I/o, Test I/o,
and Sense).
Interface Stop Signal
The Interface Stop signal is used by the channel cir-
cuitry to notify the 2702/2703 that the channel is
ending its current operation. Stop can be signaled
only during data-service cycles--i. e., when the
2702/03 is transferring a data character to the I/o
channel or, conversely, is requesting the next char-
acter from the I/o channel. It has no meaning for
commands under which no data transfers occur.
The ending procedure initiated by a Stop signal
depends on the type of terminal control and the par-
ticular command being executed.
Halt I/o (Interface Disconnect Signal)
The I/o channel signals halt to the 2702/03 with the
Interface Disconnect signal. See the I/O channel
Interface OEMI Manual, Form A22-6843. When
Halt I/O is received, the addressed line control
inhibits further data-byte transfers under the com-
mand being executed and immediately releases the
I/o channel.
If
no command is being executed, the
I/o channel is released without returning a status
byte.
The status byte sent to the channel by different
commands upon receiving a Halt I/O is shown in
Figure 2-10.
COMMANDS
Control-Type Commands
Enable
When this command is accepted, the 'enable' latch is
set within the line adapter of the addressed commu-
nications line. No data transfer occurs.
Disable
On acceptance of this command, the 2702/03 resets
the 'enable' latch within the line adapter of the
addressed communications line. No data transfer
occurs.
Sense
On acceptance of this command, the 2702/03 returns
a single byte to the channel from the sense field in
the control word of the addressed communications
line. This byte defines the condition of the addressed
communications line.
Operations
2-29

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