Siemens SINAMICS G120P, Operating Instructions Manual

Page: 228 / 496

Operation
6.8 Communication via RS485
Inverter cabinet units
228
Operating Instructions, 12/2014, A5E32923362A
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 6-19 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 6-20 Start delay and response delay
The duration of the start delay must at least be as long as the time for two characters and
depends on the baud rate.
Table 6- 19 Duration of the start delay
Baud rate in bit/s Transmission time per character (= 11 bits) Min. start delay
9600 1.146 ms > 2.291 ms
19200 0.573 ms > 1.146 ms
38400 0.286 ms > 0.573 ms
57600 0.191 ms > 0.382 ms
115200 0.059 ms > 0.117 ms
Note: The character delay time must be shorter than the start delay.