Carel pCOWeb - 8 MODBUS TCP;IP

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
•
V
ariable 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