Carel pCOWeb, User Manual

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pCOWeb +030220966 – rel. 1.1 – 12.12.2017 40
8 MODBUS TCP/IP
8.1 OVERVIEW
MODBus is a communication protocol developed by Modicon systems. In simple terms, it is a way of sending information between electronic devices. The device
requesting the information is called the MODBus Master and the devices supplying information are MODBus Slaves. In a standard Modbus network, there is one
Master and up to 247 Slaves, each with a unique Slave Address from 1 to 247. The Master can also write information to the Slaves.
8.2 BASIC DESCRIPTION
To get your modbus device working, these are the basic things you need to know:
•
Port 502 TCP (default by protocol, cannot be changed)
•
Address format: Decimal (digital number 1 = coil 1)
•
Variable bindings:

Digital variables: coils from 1 up to 2048

Analog variables: registers from 1 up to 5000

Integer variables: registers from 5001 to 10000
•
Variable types: Signed Integers (mandatory in some software to correctly
read/write the variables)
•
The ranges of variablesare aligned with the standard Modbus addresses.
•
The limits of variables are aligned with the standard Modbus limits:

read coils/discrete inputs: 2000

write coils: 1968

read registers: 125

write registers: 123
Figure 8.a - Remote connection example
8.3 COMMANDS SUPPORTED
These are the only commands supported by the pCOWeb in modbus TCP/IP

01: Read coils

03: Read holding registers

05: Write single coil

06: Write single registry

15: Write multiple coils

16: Write multiple registers

23: Read/Write multiple Registers
Figure 8.b - Protocol settings
8.4 MODBUS TCP/IP CONFIGURATION FOR pCOWeb
The page shown below summarises the Modbus TCP/IP configuration for
pCOWeb .
Available settings are:
•
Modbus TCP status: allows to enable/disable Modbus TCP/IP
communication service;
•
Modbus TCP port: configure port for protocol (default 502)
•
Map mode: it allows to adopt a different mapping scheme, to allow
retrocompatibility with older versions of
pCOWeb
.
Further explanations about mapping schemes throughout
pCOWeb
version
are available in APPENDIX J, on page 83.
Figure 8.c – Modbus TCP/IP configuration page