Temporal Sequence Of Communication - JUMO mTRON T Manual

3 Modbus protocol description
3.3

Temporal sequence of communication

Character transmission time
The character transmission time (time taken to transmit one character with 8 data bits) depends
on the baud rate and the number of bits of the character (see table for data format):
Baud rate [Bd]
Time diagram of a data request
A data request proceeds according to the following time diagram:
Master
Slave
The data request and response consist of several characters (each with a start bit, 8 data bits,
a parity
bit if necessary, and a stop bit) which are transmitted coherently.
t The slave has to observe this waiting period before sending the response
1
min.: 5 ms
typically: 5 to 35 ms
max.:35 ms or the minimum response time set in the configuration
t The master has to observe this waiting period before starting a new data request.
2
with RS232: at least 3.5 times the character transmission time (end identifier)
with RS485: 35 ms
NOTE!
The waiting periods t1 and t2 also contain the end identifier (3.5 × character transmission
time), which
follows after each data request or response.
26
Character transmission time [ms] = 1000 × number of bits / baud rate
38400
19200
9600
Data request
Number of bits
11
10
11
10
11
10
Response
t
1
Character transmission time [ms]
0,286
0,260
0,573
0,521
1,146
1,042
Data request
t
2
t