6100 BSC Programming Manual

Writing Applications that Use 6100 BSC
READ Request and Response
The READ request has several major functions, depending on
the value in the modifier field and on the line state:
• If the state is DISCONNECTED, the READ request implicitly
connects the station. The same request can accept and
acknowledge a line bid and read the first message or block.
• If the state is CIRCUIT ASSURANCE, the READ request reads the
ID of the calling station.
• If the state is CONTROL, the READ request accepts and
acknowledges a line bid and reads the first message or block.
• If the state is READ, the READ request acknowledges the
previous block with ACK 0, ACK 1, or RVI, and reads the next
message or block.
• If the state is WRITE, the READ request sends an EOT sequence
to reset the line to CONTROL state. The same request accepts
a line bid from the other station.
Each of these uses of READ has been discussed and illustrated
in this section.
The request buffer format is:
Function := 65
Modifier := 0 = send ACK 0 or ACK 1, as appropriate,
and then read the next message or block
1 = send RVI, and then read the next message or
block
If the state is CIRCUIT ASSURANCE or CONTROL,
or if this READ is intended to turn the line
around, the value must be 0.
Request ID := A unique value from 1 to 32767,
application-dependent
Text Out := 0
Text In := Maximum length, in bytes, of the message to
be read (no greater than 4096)
Text := None
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