Envoy ACP/XF Application Programming Manual

Asynchronous Balanced Mode (ABM) Protocols
EnvoyACP/XF Application Programming Manual–132179
2-5
Opening a Line
summarizes the EnvoyACP/XF error codes. This section specifies any considerations
particular to ABM.
Opening a Line
The communications line must be opened before any transmissions can take place. The
application does so by calling the OPEN procedure.
Be aware of the following restrictions on the OPEN procedure:
•
Multiple OPEN calls require that access be shared.
•
If a line is opened for exclusive access, the line can be opened only once.
•
The only other user process that can open the same line concurrently is the particular
application's backup process.
The line is opened with the number of concurrent pending nowait I/O operations set
between 0 and 15. Unless you must use a different value, use the value 15.
Setting Line Capability Characteristics
After the line has been opened, the application issues a SETMODE procedure call to
ensure that certain line characteristics are set. These characteristics are:
•
Address Verification
•
Extended Address Field
•
Extended Control Field
•
Timers and Number of Retries
•
Reject (REJ)
•
Selective Reject (SREJ)
Although you can set these characteristics during system configuration, you also should
use SETMODE to ensure that the line characteristics match the program’s requirements.
Address Verification
EnvoyACP/XF maintains two station addresses that you can modify through SCF by
using the ADDRESS modifier and subsequently alter by using the SETMODE 17
procedure. (Use the SETMODE 17 procedure only with basic address formats. For
extended address formats, use the DEFINELIST procedure. See the descriptions of
SETMODE Procedure
on page 4-13 and DEFINELIST Procedure on page 4-6.)
Defaults for these addresses are 01 and 03 (hexadecimal), respectively.
HDLC and ADCCP-ABM always include the configured address #1 in all outgoing
command frames and the configured address #2 in all outgoing response frames. HDLC
and ADCCP-ABM expect all incoming command frames to include the configured
address #2 and all incoming response frames to include the configured address #1. You