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EZwarePlus Programming Manual 237
Chapter 18Using the Modbus Gateway
The Modbus Gateway allows any ModbusTCP Master to request HMI data using standard Modbus commands. The
HMI uses the ModbusRTU/TCP Slave protocol to pass Modbus requests to any non-tag-based PLC or controller
connected to the HMI, or the HMIs internal storage.
Tag-based PLCs are those that use named tags instead of addresses, such Allen Bradley Compact and
Control Logix , Siemens S7-1200, and BACnet.
For example, the Modbus Gateway would allow a SCADA system to obtain data from a device that is not supported
by the SCADA system, but is supported by the HMI. The Modbus Gateway also allows serial-connected devices access
to the SCADA system.
The Modbus Gateway support the following Modbus function codes (decimal):
Code
Definition
1
Read Coil Status
2
Read Input Status
3
Read Holding Registers
4
Read Input Registers
5
Force Single Coil
6
Preset Single Register
15
Force Multiple Coils (LB addresses in the HMI only, not compatible with bits in a PLC)
16
Preset Multiple Registers
HMI Local Word LW9288 indicates Modbus communication errors:
Value
Error
0
No error
1
Attempt to read/write an undefined register
2
Illegal Data Value
3
Bad Command Format
4
Attempt to write to a Read-only register
5
Attempt to read to a Write-only register
6
Timeout
7
Invalid Function Code
1010-1015, Rev. 03
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