Envoy Application Programming Manual

BISYNC Centralized Multipoint Supervisor Protocol
Envoy Application Programming Manual—427159-001
4-5
ASCII and EBCDIC Line Code
The supervisor station initiates selection by calling the WRITE procedure while the line
is in a CONTROL state. This call also writes the first message to the selected tributary
station. The supervisor station must then call WRITE for each additional message to be
transmitted. When no more messages are to be transferred, the supervisor station sends
an EOT indication to the tributary station (the EOT is sent when the supervisor calls
READ to resume polling of the multipoint network). Figure 4-2
shows the selection
sequence.
ASCII and EBCDIC Line Code
An application process uses only the ASCII character set. If the line code is EBCDIC,
Envoy can be configured (by specifying the EBCDIC modifier) to perform the necessary
ASCII-to-EBCDIC translation. Envoy recognizes when transparent text is being
transmitted and does not translate the transparent text.
Retries
Line operations are subject to transmission errors in the form of BCC errors,
nonresponding remote stations, and incorrect responses from remote stations. When
these types of errors occur, Envoy retries the requested operation.
You can specify the maximum times that Envoy retries an operation after encountering
an error indication in either of the following ways:
Figure 4-2. BISYNC Multipoint Supervisor Selection
Note. Envoy does not retry the poll operation for nonresponding stations.
024CDT .CDD
No
CALL WRITE...
Send Last
Message
Last Message
to Send?
Format
Message with
Trailing ETB
1
CALL WRITE...
Send Data to
Tributary (First
Write to
Tributary
Selects the
Proper One)
2
Yes
Format
Message with
Trailing ETX