AM3270/TR3271 Reference Manual

Bisync Procedures
Bisync Protocols—Concepts and Terminology
1–8 086705 Tandem Computers Incorporated
Table 1-2. Equivalent EBCDIC and ASCII Control Characters
Bisync Control
Character (Mnemonic)
EBCDIC Control
Character
ASCII Control
Character
EBCDIC Hex
Values
ASCII Hex
Values
SYN SYN SYN 32 16
SOH SOH SOH 01 01
STX STX STX 02 02
ETX ETX ETX 03 03
ETB ETB ETB 26 17
EOT EOT EOT 37 04
DLE DLE DLE 10 10
ENQ ENQ ENQ 2D 05
ACK0
ACK1
DLE (70)
DLE /
DLE 0
DLE 1
10 70
10 61
10 30
10 31
NAK (or NACK) NAK NAK 3D 15
WACK (or WAK) DLE , DLE ; 10 6B 10 3B
RVI DLE @ DLE < 10 4C 10 3C
ITB IUS US 1F 1F
TTD STX ENQ STX ENQ 02 2D 02 05
DISC DLE EOT DLE EOT 10 37 10 04
Bisync Procedures These are the main bisync protocol procedures, and their related control characters.
Error Checking
(Block Checking)
Each message block, and each block within a multiblock transmission, contains block
check characters (BCC) after the end-of-block character (ETX, ITB, or ETB). The BCC is
placed in the trailer, which is the last part of the message block. The BCC characters
are produced as the result of error checking using one of three methods, depending
upon the code set.
As the block is received, the receiving station computes a BCC using the same method
as the sending station. At the end of the block, the receiver compares its block count
with the sender’s. If the two are not equal, a negative acknowledgement (NAK)
character is sent to the sending station, requesting retransmission. If the error
continues due to some abnormal condition such as line noise, and the maximum
number of resends is reached to transmit an error-free block, the sender will abort and
then have to establish a new connection.
The three methods of block checking for bisync are:
CRC-16—For 8-bit EBCDIC lines.
VRC/LRC—For 7-bit ASCII lines.
CRC-12—For 6-bit transmission code lines. 6-bit transmission is not supported by
AM3270 and TR3271.