Envoy Application Programming Manual

BISYNC Centralized Multipoint Supervisor Protocol
Envoy Application Programming Manual—427159-001
4-10
Address-List Format
WRITE
Transmits data to a tributary station. A call to WRITE while the line is in the
CONTROL state (an initial WRITE) causes Envoy to select the station indicated by
the entry number value in the message control word. Envoy transmits the associated
text block from the application's write buffer to the tributary station when the
tributary acknowledges the selection.
Subsequent WRITE calls while the line is in the WRITE state (continuation
WRITEs) transmit text blocks, but do not send a selection sequence. A WRITE call
completes when the selected tributary station acknowledges the message.
WRITEREAD
Performs limited conversational mode transmissions. Limited conversational mode,
in accordance with the BISYNC protocol, permits a receiving station to return text
in place of the normal positive acknowledgment to a message that ended with an
end-of-text (ETX) character. According to the BISYNC protocol, the receiving
station is permitted to return text only once before it must resume the normal
ACK0/ACK1 response sequence. The station receiving the conversational reply is
not permitted to respond with a conversational reply. The supervisor uses
WRITEREAD, when reading from a tributary station, to make a conversational
reply. The call to WRITEREAD sends a reply message to the tributary and
completes when the tributary station returns either a message or a positive
acknowledgment (if a message is returned, it is returned in the buffer specified for
WRITEREAD).
Address-List Format
The address list tells Envoy the addresses of all stations in the network that may be
polled or selected. The address list is passed to Envoy, after the line is opened and before
the first call to WRITE or READ, by a call to the DEFINELIST procedure.
This subsection includes:
•
Station Address on page 4-11
•
Poll List on page 4-11
•
Select List on page 4-12
Each entry in the address list is referred to by an ordinal entry number; the first entry is
designated entry number 0 (Example 4-1
). Envoy uses the entry number, after a READ
completion, to tell the application process which terminal responded to the poll. The
application process uses the entry number, with a WRITE call, to tell Envoy which
terminal is to be selected. The application process and Envoy pass the entry number
back and forth using the entry number field of the message control word in the
application's read or write buffer (see Message Formats
on page 4-22).