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Using the Siemens 505 PLC With The Modbus Protocol

Primary Software: Lookout
Primary Software Version: 5.1
Primary Software Fixed Version: N/A
Secondary Software:

Problem: I want to use my Siemens 505 PLC with the modbus driver object in Lookout, but the terminology seems to be very different. How can I translate between terms used in Modbus and the default protocol (TIWAY) for the device.

Solution: The following table compares the terminology used in both the Modbus and TIWAY protocols:

Modbus-based PLCs	Simatic TI PLCs
Coil	Discrete Output (Y) or Control Relay (C)
Input Register	Word Image Register (WX/WY)
Holding Register	Variable Memory (V-Memory)
Slave	Secondary Node
P/C (Programmable Controller)	PLC
Function Code	Primitive
Modbus	TIWAY 1
Disabled (coil)	Forced
Enabled (coil)	Unforced

To use the modbus protocol with this PLC, you must purchase a MODNIM, or Modbus Network Interface Module, which allows a modbus master device to access the registers of the PLC. For additional information, please refer to the Siemens Simatic TI505/TI500 MODNIM User Manual on the Siemens website linked below.

Related Links: Siemens Home Page

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Report Date: 10/21/2003
Last Updated: 10/21/2003
Document ID: 32K95QP6

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