User Manual

Communication via RS485
5.3 Communication via USS
Fieldbuses
Function Manual, 04/2018, FW V4.7 SP10, A5E34229197B AE
123
5.3.6
Time-out and other errors
You require the telegram runtimes in order to set the telegram monitoring. The character
runtime is the basis of the telegram runtime:
Table 5- 8 Character runtime
Baud rate in bit/s
Transmission time per bit
Character run time (= 11 bits)
9600
104.170 µs
1.146 ms
19200 52.084 µs 0.573 ms
38400
26.042 µs
0.286 ms
57600 17.361 µs 0.191 ms
115200
8.681 µs
0.095 ms
The telegram runtime is longer than just purely adding all of the character runtimes
(=residual runtime). You must also take into consideration the character delay time between
the individual characters of the telegram.
Figure 5-8 Telegram runtime as the sum of the residual runtime and character delay times
The total telegram runtime is always less than 150% of the pure residual runtime.
Before each request telegram, the master must maintain the start delay. The start delay
must be > 2 × character runtime.
The slave only responds after the response delay has expired.
Figure 5-9 Start delay and response delay