Modbus Rtu Library; Modbus Communication Overview; Modbus Rtu Library Features - Siemens SIMATIC S7 System Manual

Libraries

9.3 Modbus RTU library

9.3 Modbus RTU library
9.3.1

Modbus communication overview

9.3.1.1

Modbus RTU library features

STEP 7-Micro/WIN SMART includes Siemens Modbus RTU libraries. The Modbus RTU
libraries includes pre-configured subroutines and interrupt routines that make communicating
to Modbus RTU master and slave devices easier.
STEP 7-Micro/WIN SMART supports Modbus communication over RS-485 (integrated port 0
and optional signal board port 1) and RS-232 (optional signal board port 1 only) for both
master and slave devices.
Modbus RTU master instructions can configure the S7-200 SMART to act as a Modbus RTU
master device and communicate to one or more Modbus RTU slave devices. You can
configure up to two Modbus RTU masters.
Modbus RTU slave instructions can configure the S7-200 SMART to act as a Modbus RTU
slave device and communicate with Modbus RTU master devices.
Open the Libraries folder in the Instruction folder of the project tree for access to the Modbus
instructions. When you place a Modbus instruction in your program, STEP 7-Micro/WIN
SMART places one or more associated POUs in your project.
Note
Only call the library functions from either the main program or from interrupt routines, but not
both.
Note
For the compact CPU models CPU CR20s, CPU CR30s, CPU CR40s, and CPU CR60s, do
not connect pin 9 of the RS485 cable used for Modbus RTU communication. The CRs CPU
uses pin 9 to disable Freeport mode.
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System Manual, V2.3, 07/2017, A5E03822230-AF
S7-200 SMART