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Synch Characters. In asynchronous configurations open-
ing Switch V on the Keyboard Interface PCA causes SYN
characters to be inserted at the beginning of each trans-
mission and at a minimum of 1 second intervals until the
end of transmission. This allows the use of a single
generalized data communication driver for both synchro-
nous and asynchronous operation.
TRANSPARENCY MODE
(BINARY OPERA-
TION). Transparency mode allows you to send and re-
ceive 8 bit binary data. This allows the sending of data bit
patterns that might otherwise be interpreted as control
characters.
Data Communications
preceded with a single DLE character. Single DLE charac-
ters are seen as the beginning of control sequences rather
than data. The first DLE character of the above sequences
is never included in the block check.
Note that whenever control character sequences are used
in transparent mode they must have proper parity or they
will not be interpreted as control characters.
Example:
This mode is controlled with the following character
sequences:
Once in transparency mode, in order to send control char-
acters and have them interpreted as control characters
rather than binary data, the control character must be
DLE STX
DLE ETX
or
DLE ETB
DLE DLE
DLE SYN
DLE ENQ
Start transparency.
Ends transparency.
Allows one DLE character to be sent.
The bit pattern for DLE will vary with
the parity used.
Allows one SYN character to be sent (for
synchronous operation). Not included in
text or BCC.
Aborts current transmission. A BCC
character is not expected.
These characters are not included in the block check
/
/
/
\
~ ~
<data)
~ ~
<data)
~
!i"
<data)
~
Fx
Bee
PAD
\
/
Begin block check
End block check
The terminal will always accept transparent data. Escape
sequences can be used to cause it to transmit transparent
data. The Z strap can also be used to cause the transparent
transmission of all data at all times (permanent transpar-
ent text OUT mode).
BLOCK PROTOCOL CONTROL SEQUENCES
Block protocols require specific control sequences to
acknowledge text block transfers, terminate text transfers
or to inform the sender or receiver of status changes.
These sequences consist of one or more data link control
characters. A list of these control characters are given in
table 5-10. A summary of the uses of these characters is
gi ven in table 5-11.
Figure 5-12 illustrates the operation of the various control
characters used in the block protocol.
5-29
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