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Configuring the Modbus Models
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Timeout Examples
Here are some examples for setting the link timeout value. Each is
based on a Modbus message transaction of 256 bytes to the port device
and 256 bytes from the device.
V Parameters: RTU, 9600 baud, 1 start, 8 data, no parity, 1 stop.
Serial communication time: (10Ăbits)/9600 = 1.04 ms/character,
267 ms for 256 bytes (RTU mode sends one character per byte).
Slave controller scan time: 100 ms.
BM85 time: 4 ms.
Total time: (267Ă+Ă267Ă+Ă100Ă+Ă4) = 638 ms.
Use a link timeout value of 10 (1000 ms).
V Parameters: ASCII, 9600 baud, 1 start, 8 data, 1 parity, 1 stop.
Serial communication time: (11Ăbits)/9600 = 1.15 ms/character,
294 msĂxĂ2 = 588 ms for 256 bytes (2 chars/byte for ASCII).
Slave controller scan time: 100 ms.
BM85 time: 4 ms.
Total time: (588Ă+Ă588Ă+Ă100Ă+Ă4) = 1280 ms.
Use a link timeout value of 15 (1500 ms).
V Parameters: ASCII, 300 baud, 1 start, 8 data, 1 parity, 2 stop.
Serial communication time: (12Ăbits)/300 = 40 ms/character,
10.24 secondsĂxĂ2 = 20.48 s for 256 bytes (2 chars/byte for ASCII).
Slave controller scan time: 100 ms.
BM85 time: 4 ms.
Total time: (20.48 sĂ+Ă20.48 sĂ+Ă100ĂmsĂ+Ă4Ăms) = 41.06 s.
Use a link timeout value of 450 (45000 ms, or 45 s).