CP340做MODBUS从站程序

This Applications Tip describes a method for getting an S7-300 family PLC to act as a Modbus
RTU secondary device. This tip will not work for S7-400 PLC’s because the current versions of
the CP441 card (6ES7 441-1AA00-0AE0 and 6ES7 441-2AA0-0AE0) do not support the ASCII
driver.
Hardware Requirements:
·  S7-300 PLC. The Modbus and CP340 code and data size is about 7 Kbytes, so a S7-313 or
better is required.
·  CP 340 Point-to-Point Communications Processor
Supported Functions:
·  Modbus Function 3 - Read Holding Registers
·  Modbus Function 16 - Preset Multiple Registers
Both of these functions map Modbus holding registers starting at Modbus address 40001 into a
single S7 data block.