User`s guide
40 DC 900-1340I
BSC Programmer’s Guide
The maximum size for a 3780 text block is 512 bytes including the STX and ETX char-
acters. BSC 3780 also allows for compression of two or more consecutive space charac-
ters within the text block. Consecutive spaces are replaced with a GS character (IGS in
EBCDIC) and a count character. More information on the BSC 3780 protocol can be
found in the IBM document, Component Description: IBM 3780 Data Transmission Ter-
minal.
2.3.3 Transmission Codes
The Protogate BSC software can transmit and receive data in either the American Stan-
dard Code for Information Interchange (ASCII) character set or the Extended Binary
Coded Decimal Interchange Code (EBCDIC) character set depending on the setting of
the BSC character set option (Section 6.7 on page 162). The data transferred between
the client program and the BSC software is always in ASCII and is translated by the BSC
software as required.
2.3.4 Messages and Transmission Blocks
The client computer sends data to the BSC software as complete messages. A message
consists of one or more buffers of text or binary data. The BSC control characters are
not included in the message. The control characters are inserted by BSC before trans-
mitting the data. Once in memory, the messages may be transmitted in smaller blocks,
Figure 2–3: Normal 3780 Text Block
Figure 2–4: Transparent 3780 Text Block
SYN SYN STX record RS record record ETX BCC PADRS
SYNSYN STX record RS record record ETX BCC PADRSDLE RS DLEDLE
DLE
DLE