AM3270/TR3271 Reference Manual

Control Characters
Bisync Protocols—Concepts and Terminology
086705 Tandem Computers Incorporated 1–7
Table 1-1. Bisync Transmission Control Characters (Page 2 of 2)
Bisync Control
Character
(Mnemonic) Function Action and Response(s)
ITB Intermediate block
character
Separates long message blocks into sections for error
detection without causing a reverse of transmission
direction. Indicates block check is next, and resets
counter to zero.
The receiver does not respond until it receives a final
block containing an ETB or ETX.
Intermediate blocks do not need to start with STX
unless they are the first intermediate block or they
divide a heading block from a text block.
TTD Temporary text delay Indicates the sender is not ready to transmit but wants
to retain the connection because it expects to be ready
momentarily.
The receiver responds with a NAK. The sender sends
another TTD if still not ready.
EBCDIC and ASCII Control
Characters
Table 1-2 lists the bisync control characters that appear in Table 1-1, and shows their
control character equivalents in EBCDIC and ASCII code sets. Since EBCDIC and
ASCII do not provide codes for some of these control characters, the codes have been
created by combining existing characters into two-character sequences, as shown in
the following table.