NOTE: For World Trade operation when using Telegraph Term­
inal Control Type 1, this status indicates that the End of
Block (£OB) signal was received--that is, "FIGS-X" (upper­
case X). Channel End, Device End, and Unit Exception
The conditions that cause this status to be signaled
depend on both the type of line and terminal control
involved, as well as the particular command that
was issued. It w ill never be signaled for Disable,
Break, or Sense. For the remaining commands, this
status indication is influenced by the type of terminal
control involved, as follows: 30 Read vi Inhibit Search Write
or Poll Tenllinal C011Lrvi Ty}?c: 1. This
status is signaled if (Q (EaT) or ® (negative reply) is received while the
addressed linc is in control mode and
executing either of these conunands. It is also set any time a © is received,
providing the 2741 Break feature is not
installed.
IBM Terminal Control Type II. This
status is signaled if ® is received
while the addressed line is executing
either of these commands and the line
is in control mode. It is also set any
time a © is received.
Telegraph Terminal Control Type I. Operating with 83B2/83B3 and 115A
terminals, tIlis status is set if the End
of Transmission signal (FIGS- H, LTRS) is received while the addressed
line is executing either a Read or
Inhibit command.
Telegraph Terminal Control Type II.
This status means that the EOT character was received while executing
either of these commands.
World Trade Terminal Control. This status means that the EOT sequence was received while
executing either of tilese commands.
Telegraph Terminal Control Type I
(only). With either 83B2/83B3 or
115A terminals, this status indicates
that the EaT sequence (FIGS-H, LTRS) was received while executing this
command.
This status is signaled if the receive­
control bit in the addressed MCW-l is ON when the command is accepted. The r:om mand' s execution is termina­
ted immediately. Dial
Prepare Enahlp Wrap
If Halt I/O is signaled during the execu­
tion of Dial, before Stop was received
from the I/O channel (the entire
number has not been dialed), the Dial
operation is ended with this status.
If Halt I/O is issued to a line that is
executing Prepare, and the line has
started to receive (a true start bit
was detected) but the ending status
has not yet been signaled, then this
status is signaled at the normal ending
point for this command, after the line
returns to Mark. This statue: is signa1ed if Halt Tla is
issued to a line that is executing
Enable and the call has not yet been
answered (Data Set Ready is OFF). The 'enable' latch is reset.
This status will be signaled if the
receive-control bit in the addressed MCW-l is ON when the Wrap command
is accepted. 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 cause the
command to end with Channel End, Device End, and Unit Exception status plus one or more of the error
conditions that cause the sense bits to. be set. A Sense command should be issued to the unit address
.in order to determine the error conditions. The
conditions that can be signaled are listed under "Sense-Byte Conditions." This status can be signaled
only when ending Wrap, Read, Write, Dial, Prepare,
Enable, Inhibit, Search, or Poll. Channel End, Device End, and Unit Check This status indicates that the current command has
been ended by an error or an unusual condition. A Sense command must be issued to the addressed unit
to further define these conditions. Channel End, Device End, and Status Modifier
This status is set for the Poll command when a @ (EOA) character is detected. SENSE - BYTE CONDITIONS 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 I

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