different sense conditions, as indicated by the
following chart. The sense byte is assembled within
the MCW-2 and transferred to the processor, by way
of the multiplexer channel, when requested by the
Sense command.
Bit Positions
(within Sense Byte)
o
1
2
3
4
5
6
7
Sense Conditions
Command Reject
Intervention Required
Bus Out Check
Equipment Check
Data Check Overrun Lost Data
Timeout
Four of these sense bits (2, 3, 5, 6) are set by
the common controls independent of the specific
terminal control associated with the addressed line.
The other four sense bits (0, 1, 4, 7) are associated
with the terminal control for the line.
The sense information pertaining to the previous I/O op:;ration is reset by the next command addressed
to a line (except for I/O No-Op, Halt I/O, Test I/O, and Sense).
Common Controls
The various sense conditions are:
2-Bit--Bus Out Check
This bit is set when a parity error is detected on Bus Out. Parity is checked on Bus Out when the command
is transferred during initial selection, and when out­
put data (from the channel) is being presented.
The command terminates at the normal ending time.
The 2703 will not respond to initial selection unless
the address on Bus Out has correct parity.
3-Bit--Equipment Check
This bit is set when a check condition has been
detected within the 2703. These conditions are:
1. A transfer check of the 'transmit data' latch
occurred within a line adapter during execution
of Write, Break, Poll, or Wrap. 2. A transfer check of the 'enable' latch occurred
during execution of Enable, Dial, or Disable.
3. A transfer check of the 'call request' latch
occurred during the Dial command.
4. If a line is in operation and a new command
is issued for that line, Equipment Check is
returned and the-previous operation will be
terminated immediately.
5. A core-storage parity error occurred when a
command was present in the line.
6. A delay-line malfunction occurred for all lines
of the associated base with a command
present.
5- Bit--Overrun This bit is set under the Read or Inhibit commands
during a receive operation, if a byte of data is lost
because data service could not be obtained within the
one-character interval of the communications line-­
that is, if data service is not honored by the channel
before the stop bit for the next character is received.
This sense bit is never set while executing any
command other than Read or Inhibit.
6-Bit--Lost Data
This bit is set during either a Read, Inhibit, Prepare,
or Search command as follows:
1. During a Read command if the command is
issued to a line whose data-service bit in the MCW-1 is set. This indicates a loss of data,
since the command was not issued within four
characters of the time the line became active.
2. Also during a Read command if the data­
service bit in the MCW-1 is ON when the line
receives a Halt I/O command.
3. If a stop sequence is indicated by the channel
while in a read-service operation.
4. During a Read, Inhibit, Search, or Prepare
command if the receiving bit in the MCW-1 is ON when a Halt I/O is issued.
5. In case the receiving bit in MCW-I is ON when l
a Search is issued.
6. If a Dial command is issued to a line already
"off-hook. " 7. If the PND (present next digit) lead from the
Automatic Calling Unit is ON while the sequence
field (in MCW-I) is in the reset state.
All these conditions indicate a possible loss of data.
IBM Terminal Control Type I 0- Bit--Command Reject
This bit is set during initial selection:
1. By the interface controls if a command that is
not defined or cannot be executed by the 2703 is presented. This occurs if the Dial command
is issued and the Autocall Adapter has not been
installed in the 2703. The Dial command is 31

accepted, but then rejected if issued to a line
not associated with an installed Autocall
Adapter.
2. By the common controls if an associated line is
issued the Break or Search command. The
Break or Search is not executed, but is ended
immediately.
This sense bit is never set for the Read, Write, Poll, Prepare, Wrap, Enable, Disable, Inhibit, or
Sense commands.
1-Bit--Intervention Required
If a Read, Inhibit; Poll; Write, or Prepare command
is being executed and the addressed line has a data
line set attached, this bit will be set:
1. If the data set has power off.
2. If the data set is not attached to the 2703.
3. If the data set is either "on-hook" or not in
data mode.
4. If the addressed line has a telegraph line
adapter that has not been enabled.
5. For the Read, Inhibit, and Poll commands
only, if a continuous Space signal is received
for one character time or greater.
6. While Dial is being executed, if the ACU (Automatic Calling Unit) Power Indicator is OFF. 7. Also if the ACU is not connected to the 2703.
This bit is never set under the Wrap, Enable,
Disable, and Sense commands.
4-Bit--Data Check
This bit is set:
1. During execution of the Read and Inhibit
commands if the line is in text-out mode and
a ® (negative reply) is received; it indicates
that the remote terminal reGeived data with
incorrect parity or LRC.
2. For the Read, Inhibit, and Poll commands if
the line is at Space at stop-bit time (2703 is
out of sync).
3. When the line is executing Write, Poll, or Wrap if a VRC error is detected in one of the
characters being transmitted.
4. If the line is equipped with the telegraph line
adapter and an echo chp-ck occurs.
5. During Read, Inhibit, or Poll when a VRC or
LRC error is detected.
6. If the response to a Poll command is not @ or ®. This sense bit is not set during the execution of
Dial, Prepare, Enable, Disable, or Sense.
32
7 -Bit--Timeout
This sense bit is set:
1. During the execution of the Read command if
no characters are received for a continuous
period of three seconds while the line is in
control mode. For text-mode operation, a
28-second timeout applies.
2. During the execution of Dial, if the ACU's ACR (Abandon Call and Retry) line turns ON. This indicates that the call was not established
in the allotted period of time and should be
redialed.
3. During a Poll command if no characters are
received for a continuous period of three
seconds when the receive-control bit is ON. 4. During the execution of a Prepare command if
a continuous Space signal has been received
for more than 28 seconds.
5. During the execution of Disable if a switched­
network data set does not go "off-hook" or "on­ hook" within 28 seconds after being signaled to
do so. That is, Data Set Ready does not turn OFF and end the Disable command within 28
seconds of the time that Data Terminal Ready
turned OFF. This sense bit is not set during execution of Write, Wrap, Break, Enable, or Sense.
IBM Terminal Control Type II
O-Bit--Command Reject
This bit is set during initial selection:
1. By the interface controls if a command that is
not defined or cannot be executed by the 2703
is presented. This occurs if the Dial command
is issued and the Autocall Adapter is not
installed in the 2703. The Dial command is
accepted but then rejected when issued to a line
not associated with an installed Autocall
Adapter.
2. By the common controls if an associated line
has been issued the Break or Search command.
The Break or Search is not executed but is
ended immediately.
This sense bit is never set for the Read, Write Poll, Prepare, Wrap, Enable, Disable, Inhibit,
or Sense commands.
1-Bit--Intervention Required
This bit is set when a Read, Inhibit, Poll, Write, or Prepare command is being executed and the addressed
line has a data line set attached: I