CCMMUNICATIONS SECTION 6.7
6. 7. 3 BINARY SYNCHRONOUS COMMUNICATIONS (B.SC)
6.7.3.1
6.7.3.2
6.7.3.3
VER. V09l''
The information carrier for 2780 is the binary synchronous
communications (BSC) procedure. The character set used is
EBCDIC (Extended Binary Coded Decimal Interchange Code). The
following is a description of the subset of BSC used for HUNTER
2780 enulation.
NOTE: HUNTER generally operates using the USACII (United States
of America Standard Code for Information Interchange). Charac-
ters either transmitted or received by Basic will be
in ASCII,
so CHR$, LOPCHR, etc., instructions all generate ASCII charac-
ters. To use EBCDIC the 2780 driver software utilises an ASCII
to EBCDIC and EBCDIC to ASCII code converter. The conversions
used are listed in section 9.11, ASCII TO EBCDIC CONVERTION.
The code used on the transmission channel is transparent to
Basic programs, and need not concern the programmer.
Text Blocking
BSC defines general structural procedures for the blocking of
information. Several control characters are used for the
control of message blocks.
A message consists of one or more blocks of text data. The
start of text character (STX) is used immediately preceeding
each block of data. Each data block but the last is terminated
by an end of transmission block (ETB) character or an
intermediate text block (ITB) character. The last data block
ends with an end of text (ETX) character.
Error Checking
Each block of data is error checked by the receiver by a cyclic
redundancy check (CRC). After each transmission the receiver
normally replies with ACKO or ACK1 - data accepted continue
sending; of with NAK - data not accepted (e.g. due to a data
transmission error), retransmit the previous block.
CRC-16
HUNTER uses the accepted error checking method of EBCDIC 2780.
The cyclic redundancy check is a division at both the
transmitting and receiving stations using the numeric value of
the message as a dividend, divided by a constant. The quotient
is discarded and the remainder is used as the check character.
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