21: DATA LINK COMMUNICATION
OPENNET CONTROLLER USER’S MANUAL 21-9
The communication sequence in the separate refresh mode is shown below:
Separate Refresh Time at Master Station for Communication with One Slave Station (Trf)
When the baud rate is set at 19200 bps, the master station requires the following time to refresh the transmit and receive
data for communication with one slave station.
Trf = 2.083 msec × (Transmit Words + Receive Words) + 3.125 msec + 1 scan time
Total Separate Refresh Time at Master Station for Communication with All Slave Stations (Trfn)
When the baud rate is set at 19200 bps, the master station requires the following time to refresh the transmit and receive
data for communication with all slave stations, that is the total of refresh times.
Trfn = ∑ Trf = ∑ {2.083 msec × (Transmit Words + Receive Words) + 3.125 msec + 1 scan time}
Example: Refresh Time in Separate Refresh Mode
When data link communication is performed with such parameters as transmit words 10, receive words 10, slave stations
8, average scan time 20 msec, and baud rate 19200 bps, then the total refresh time Trf8 for communication with all eight
slave stations in the separate refresh mode will be:
Trf8 = {2.083 msec × (10 + 10) + 3.125 msec + 20 msec} × 8 = 518.28 msec
When the baud rate is 38400 bps, the total refresh time will be:
Trf8 = 518.28 msec ÷ 2 = 259.14 msec
Master Station
1 scan time
END Processed
Slave 1
Refresh
Slave 1 Comm.
Completion M8140
Slave 2 Comm.
Completion M8141
Slave 31 Comm.
Completion M8176
All Slave Comm.
Completion M8177
1 scan
Slave 1 Comm.
Completion M8140
END Processed
Slave Station 1
Master
Station
Slave
Station
1
1 scan time
Slave 2 Comm.
Completion M8141
Slave Station 2
Slave
Station
2
1 scan time
Slave 31 Comm.
Completion M8176
Slave Station 31
Slave
Station
31
END Processed
END Processed
Slave 2
Refresh
Slave 3
Refresh
Slave 31
Refresh
Slave 1
Refresh
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