CTI 2572-A, Installation And Operation Manual

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CTI 2572-A Installation and Operation Guide V1.3 53
CHAPTER 6. MODBUS TCP SERVER
6.1. Configuration
The Modbus TCP server starts automatically. There is no configuration or startup logic required.
6.2. Variable Mapping
Modbus TCP uses a different nomenclature than the SIMATIC® 505 to describe data elements. The
following table provides a cross reference.
Modbus Variable 505 PLC Equivalent Variable
Coil Control Relay (C )
(Discrete) Input Discrete Input (X)
Holding Register User Variable Memory (V)
Input Register Word Input (WX)
Modbus data elements are referenced to 0, while 505 data elements are referenced to 1. Thus, the first
Modbus Holding Register is Register 0, while the first 505 V memory location is V1.
NOTE:
Some Modbus TCP client software may start with holding register 0. To be sure how your client will
work, you should test your application.
6.3. Supported Modbus Function Codes (FC)
The following Function Codes are supported by the Modbus/TCP Server function.
FC
(dec)
FC
(hex)
Function Codes 505
Variable
Comments
01 01 Read Coil Status C Max number of coils = 2000
02 02 Read Input Status X Max number of inputs = 2000
03 03 Read Holding Register V Max = 125
04 04 Read Input Register WX Max = 125
05 05 Write Single Coil C
06 06 Write Single Register V
07 07 Read Exception Status C TBD. This returns Y1-8 or C1-8 in
2573-MOD.
15 0F Write Multiple Coils C Max = 800
16 10 Write Multiple Registers V Max = 100