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Examples of Use of Special Characters
Figure 2-27 shows the use of special characters is
sample messages.
Modes of Operation
The IBM Terminal Control Type II can be set in one
of the following modes.
Control Mode. The IBM TC-II is set in control mode
when it transmits the
©
character. The adapter
is in control mode when polling or addressing.
Text-Out Mode. The IBM TC-II is set in text-out
mode when a
@
character is transmitted. The
IBM TC-II remains in text-out mode during ensuing
read-type operations. Text-out mode is reset only
when a
©
is transmitted or received or an I/O reset
is given.
Text-In Mode. The IBM TC-II is set in text-in mode
when a
@
character is received from the communi-
cations line. The terminal control remains in text-
in mode during read-type operations. Text-in mode
is reset when a
©
is transferred from the channel
or an I/O reset is given.
Timeouts
Immediately following the issuance of the Read com-
mand, when the IBM TC-II is in control mode, the
normal 28-second line timeout is pre-empted by a
3-second short timeout. Once the first character
is received, the timeout period between characters
reverts to 28 seconds during execution of the Read
command.
IBM WORLD TRADE TELEGRAPH TERMINAL
CONTROL
The IBM World Trade Telegraph Terminal Control
is designed to service World Trade Teleprinters.
Transmission Code
The shifted Baudot code is used between the 2702
equipped with the WT Telegraph Terminal Control
and the WT Teleprinters.
Figure 2-28 shows the
transmission code. One start bit and two stop bits
are transmitted by the 2702. The 2702 checks for
one start bit and at least one stop bit on a receive
operation. The start and stop bits are added to or
deleted from the character by the 2702.
Transmission Code Converted to Interface Code
Figure 2-29 shows the conversion between the I/O
interface code and the transmission code. Interface
byte position 2 represents the shift bit of the charac-
ter. A one in the shift bit position represents a
Figures shift, while a zero represents a Letters
shift.
On a transmit operation (write-type operation),
the 2702 monitors the shift bit of the data bytes
received from the I/O interface. When the 2702
detects a change in the shift bit between two charac-
ters, the terminal control inserts the proper shift
character (LTRS or FIGS) between the two characters
as it sends the characters to the communications line.
On a receive operation (read-type operation), the
2702 keeps track of the last shift character
received from the communications line and inserts
zeros or ones into the I/O interface bit position 2
to give the interface character the proper shift.
The terminal control is automatically set to lower
case (LTRS) whenever the 2702 is reset.
Special Characters
The IBM World Trade Telegraph Terminal Control
detects certain character sequences as special
characters (Figure 2-30). These sequences (a FIGS
shift, a preassigned character, and a LTRS shift)
are recognized as an EOT or EOB character.
Transmit
The following characters are recognized during
write-type operations.
LTRS (Letters shift). In FIGS mode, any character
with the shift bit set to zero causes the terminal
control to send the LTRS character and sets LTRS
mode before it is transmitted.
If
wired for the Downshift on Space (a special
feature) operation, the space character sets LTRS
mode and the 2702 sends the LTRS character.
this case, the shift bit accompanying the space
character is ignored.
FIGS (Figures shift). In LTRS mode, any character
with the shift bit set to one causes the 2702 to
send FIGS character and set FIGS mode before it is
transmitted.
Receive
The following characters are recognized during
read-type operations.
Operations
2-45
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