Watlow Silver Series - Manual (Page 200)

192 EZware5000 Series Programming Manual
Chapter 13 – Using 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
1010-1007, Rev. 10