Connection to a fieldbus
6.4 Communication via RS485
Inverter with CU240B-2 and CU240E-2 Control Units
Operating Instructions, 07/2010, FW 4.3.2, A5E02299792B AA
147
6.4.3.3
Baud rates and mapping tables
Permissible baud rates and telegram delay
The Modbus RTU telegram requires a pause for the following cases:
● Start detection
● Between the individual frames
● End detection
Minimum duration: Processing time for 3.5 bytes (can be set via p2024[2]).
A character delay time is also permitted between the individual bytes of a frame. Maximum
duration: Processing time for 1.5 bytes (can be set via p2024[1]).
Table 6- 29 Baud rates, transmission times, and delays
Baud rate in bit/s (p2020) Transmission time per
character (11 bits)
Minimum pause
between two
telegrams (p2024[2])
Maximum pause
between two bytes
(p2024[1])
4800
2.292 ms
≥ 8.022 ms
≤ 3.4380 ms
9600
1.146 ms
≥4.011 ms
≤ 2.1900 ms
19200 (factory setting)
0.573 ms
≥ 2.0055 ms
≤ 0.8595 ms
Note
The factory setting for p2024[1] and p2024[2] is 0. The particular values are pre-assigned
depending on the protocol selection (p2030) or the baud rate.
Modbus register and Control Unit parameters
Since the Modbus protocol can only handle register or bit numbers for addressing the
memory, assignment to the appropriate control words, status words and parameters is
performed on the slave side.
To ensure compatibility with the Micromaster MM436, two address areas are supported.
MM436
40001 … 40065
SINAMICS G120
from 40100 to
40522
The valid holding register address area extends from 40001 to 40522. Access to other
holding registers generates the fault "Exception Code".