6100 BSC Programming Manual

6100 BSC Concepts and Context
TRANSPARENT TEXT. An application might want to include as
message data a bit pattern corresponding to a BSC control
character. For example, a message could contain numerical
results of computations, an object file, or digitized
graphic material. In such a case, a sequence of bits
intended as data might coincidentally match the value of a
character like STX or ITB. To provide for these situations,
BSC has a feature called transparent text mode. The message
formats for transparent text mode are shown in Figure 1-7.
An application initiates transparent text mode by inserting
the character DLE before the STX that starts the block.
DLE, or Data Link Escape, has a value of 10 hexadecimal in
ASCII or EBCDIC. When a block begins with DLE STX, BSC
proceeds as follows:
• It inserts a DLE before the ETB or ETX that ends the block.
• It inserts a DLE before any DLE that occurs as data in the
message text.
• Instead of inserting SYN SYN every second within a message,
BSC inserts DLE SYN.
The block check accumulation doesn't include the DLE characters,
except a DLE that occurs as data in the message text.
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