Envoy Application Programming Manual

BISYNC Point-To-Point Protocol
Envoy Application Programming Manual—427159-001
3-31
CONTROL Procedure (Send EOT)
CONTROL Procedure (Send EOT)
The EOT sequence is used to relinquish line control or to reset the line following a
READ error. The application sends EOT by calling the CONTROL procedure and
specifying operation 13 (Example 3-13
).
CONTROL Procedure (Send WACK)
The WACK sequence is used following a READ or WRITEREAD to indicate a
temporary not-ready condition to the sender while maintaining the communications link.
The application sends WACK by calling the CONTROL procedure and specifying
operation 14 (Example 3-14). In the SWIFT protocol, up to 30 consecutive WACK
sequences can be issued; if a station receives 31 WACK sequences, it drops the
communications link.
CONTROL Procedure (Enable RVI)
The RVI sequence is used by the secondary station before a READ to inform the
primary station that the secondary station has data to send and would like to bid for the
line. This operation causes an RVI to be sent to the primary in lieu of the normal
ACK0/ACK1 sequence when the next READ is performed. Enable RVI is permitted
only once, while the secondary is in the READ state. The application enables RVI by
calling the CONTROL procedure and specifying operation 15 (Example 3-15
).
Example 3-13. CONTROL Procedure (Send EOT)
CALL CONTROL(fnum,13)
| EOT -->
|
|
(CONTROL completes)
error = 0
line state = CONTROL
Example 3-14. CONTROL Procedure (Send WACK)
CALL CONTROL(fnum,14)
| WACK -->
| <-- ENQ
|
(CONTROL completes)
error = 0
line state = READ
Example 3-15. CONTROL Procedure (Enable RVI)
CALL CONTROL(fnum,15)
CALL READ
| rvi -->
|
V