4 Modbus protocol description
16
4.3 Timing of the communication
Character
transmission
time
Start and end of a data block are marked by transmission pauses. The
character transmission time (time required to transmit one single character)
depends on the baud rate and the data format used.
For a data format of 8 data bits, no parity bit and one stop bit, this is:
Character transmission time [ms] = 1000 * 9 bit ÷ baud rate
For the other data formats, this is:
Character transmission time [ms] = 1000 * 10 bit ÷ baud rate
Example
Timing scheme A data request runs according to the following timing scheme:
Baud rate [baud] Data format [bit]
character transmission
time [ms]
38400
10 0,260
9 0,234
19200
10 0,521
9 0,469
9600
10 1,042
9 0,938
t
1
Internal waiting time of the paperless recorder prior to checking
the data request and the internal processing time.
min.: 5 ms
typical: 5 ... 45 ms
max.: 60 ms or set "minimum response time"
Master
Slave
Data request
Response
Data request
t
t
1
t
2
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