6100 BSC Programming Manual

6100 BSC Concepts and Context
• After sending a message or block to which an acknowledgement
is expected, a station waits for a prescribed interval before
retrying the transmission. The interval is 2.7 seconds for
a primary station, 3 seconds for a secondary station. This
difference ensures that if transmissions collide, the retry
by the primary occurs before the retry by the secondary.
NOTE
6100 BSC lets you set up a link in which both stations
are primary, or both are secondary. In the first case,
contention for the line is resolved when one station
exhausts its retries; in the second case, contention is
resolved when one station yields the line to the other.
Both configurations waste processing time and should be
avoided.
1
2
3
4
Secondary
Station
S5066-001
"I want the line"
"I want the line"
"I want the line"
"Okay. You win."
Secondary
Station
Both stations wish to transmit data.
Legend
P
A
D
S
Y
N
S
Y
N
E
N
Q
P
A
D
P
A
D
S
Y
N
S
Y
N
E
N
Q
P
A
D
P
A
D
S
Y
N
S
Y
N
E
N
Q
P
A
D
P
A
D
S
Y
N
S
Y
N
A
C
K
P
A
D
0
1
2
3
4
The secondary station finds out the other station is bidding.
Request completes with status 166.
BSC retries the request for the primary station.
The secondary station yields the line.
Primary
Station
Figure 1-2. Primary and Secondary Stations
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