Envoy ACP/XF Application Programming Manual

Normal Response Mode (NRM) Protocols
EnvoyACP/XF Application Programming Manual–132179
3-16
Transferring Frames
Your application uses the DEFINELIST procedure call to pass the station list to
EnvoyACP/XF. EnvoyACP/XF refers to the specified addresses of multipoint tributary
stations by using a station index in the second byte of the Message Control Word
(MCW) in the READ or WRITE buffer. The station index refers to the order in which
the DEFINELIST procedure call defines the station addresses.
A supervisor application uses a READ call to initiate polling. When the READ
procedure completes, EnvoyACP/XF uses the station index to indicate to the application
which station address caused the completion.
For the WRITE and WRITEREAD procedures, a supervisor application uses the station
index to designate the tributary to which a particular frame is sent.
In a supervisor station, the CHANGELIST procedure allows your application to perform
the following tasks:
•
Enable or disable the polling of a particular station.
•
Alter the polling type (continuous or noncontinuous) previously specified through a
DEFINELIST procedure.
•
Resume the polling of stations that are in an error stop state.
In a multipoint tributary, a CHANGELIST procedure call activates or deactivates one or
all of that tributary’s station addresses. Refer to the CHANGELIST procedure in the
Guardian Procedure Calls Reference Manual for additional information.
Transferring Frames
SDLC and ADCCP-NRM use three types of frame format:
•
Information frame (I-frame) which transmits application-level data
•
Supervisory frame (S-frame) which coordinates line use
•
Unnumbered frame (U-frame) which coordinates line use
You also can use a U-frame to transmit application-level data if you do not want the
particular frame to be checked for frame sequencing.
Each WRITE call results in the transmission of one frame. You generally use the
WRITE call to transmit data in the form of numbered I-frames. For this kind of call, you
supply the address of an application buffer containing the data to be transmitted, as well
as a count parameter specifying the number of bytes in the buffer.
Note. EnvoyACP/XF continues to poll as long as a READ is outstanding. Noncontinuous
polling means that EnvoyACP/XF notifies the application when a specified number of polling
cycles has been reached. When you specify the polling types as continuous, EnvoyACP/XF
does not notify the application regarding the completion of polling cycles.