Envoy Application Programming Manual

BISYNC Multipoint Tributary Protocol
Envoy Application Programming Manual—427159-001
5-20
Line Action by Procedure Call
Line Action by Procedure Call
This subsection describes the BISYNC control sequences transmitted because of calls to
file-system procedures. It also describes the actions of file-system procedures in
response to line states and the reception of selected control sequences.
This subsection includes:
•
READ Procedure on page 5-20
•
READ-Type Bit on page 5-25
•
WRITE Procedure on page 5-26
•
WRITEREAD Procedure (Conversational Exchange) on page 5-27
•
CONTROL Procedure (Send EOT) on page 5-28
•
CONTROL Procedure (Send WACK) on page 5-29
•
CONTROL Procedure (Send TTD) on page 5-29
READ Procedure
The READ procedure is used to initiate the polling sequence and to read messages
containing data from a responding tributary station. While messages are being read, the
line is in the READ state. The line returns to the CONTROL state when the tributary
station sends an EOT sequence (to indicate the completion of the transmission).
Initial READ (Line in CONTROL State)
An initial READ causes Envoy, on behalf of the application process, to monitor the line
for polling and selection sequences.
If a station whose poll-state bit is inactive is polled (Example 5-3
), Envoy responds to
the poll with an EOT sequence (the READ does not complete). If a station whose poll-
state bit is active is polled, the READ completes with the address-list entry number of
the polled station placed in message control word bits 8:15. A condition code of CCL is
also returned and the line is in a WRITE state. A subsequent call to FILEINFO returns
an error 166 (ENQ received).