Envoy Application Programming Manual

BISYNC Multipoint Tributary Protocol
Envoy Application Programming Manual—427159-001
5-21
READ Procedure
If a station whose select-state bit is inactive is selected, Envoy responds to the selection
sequence with an RVI sequence (the READ does not complete).
If a station whose select state is active is selected (Example 5-4
), Envoy responds to the
selection sequence with an ACK0/ACK1 sequence. The READ completes when the
initial message is received from the supervisor station. The successful receipt of the
initial message is indicated by a condition code of CCE on return from the READ. The
address-list entry number of the selected station is returned in the message control word,
bits <8:15>, the initial message is returned in the line buffer of the application process,
and the line is in the READ state.
Example 5-3. Initial READ (Line in CONTROL Inactive State)
Tributary (Local) Supervisor (Remote)
line state = CONTROL
all select addresses = inactive
CALL READ(...)
| <-- EOT SYN-poll addr 1-ENQ
| EOT -->
| <-- EOT SYN-poll addr 2-ENQ
| EOT -->
|
poll address 1 set active
using CHANGELIST
|
| <-- EOT SYN-poll addr 1-ENQ
(Initial READ completes)
error = 166
line state = WRITE
MCW.<8:15> contains entry number for station = poll addr 1