Siemens SENTRON PAC3120, Manual, Page: 31 / 160

Description
2.5 RS485 interface PAC3120 and PAC3220 only
PAC3120 and PAC3220
Equipment Manual, 10/2019,
L1V30425208F-01
29
2.5 RS485 interface PAC3120 and PAC3220 only
RS485 interface for Modbus RTU communication
The PAC3120 is equipped with an RS485 interface for Modbus RTU communication. The
device operates as a Modbus slave.
Application
This interface permits:
● Reading out the measured values
● Reading and writing the device settings
● Updating the device firmware
The Modbus function codes are listed in the Appendix.
Conditions for operation
To use the interface, the device must be parameterized in accordance with the existing
Modbus infrastructure. The communication parameters can be set on the device and via the
Modbus RTU interface.
Default communication settings
In the as-delivered state, the following default values are set:
Table 2- 3 Default Modbus RTU communication settings
Setting Default value
Address 126
Baud rate 19200
Data format 8N2
Response time 0 (automatic)
Delaying the response time
The response time of the PAC3120 may have to be delayed to enable its operation as a
slave device with devices from other manufacturers on the bus. The PAC3120 can
automatically calculate the response time to suit the baud rate. This automatic calculation is
set at the factory. The delay time is individually adjustable between 1 ms and 255 ms.
Polarization
Polarization of the RS485 data lines must be implemented at another point on the bus. The
PAC3120 does not contain polarization resistors.