Modbus Interface
CoolPlug PRM Rev 0.1
4
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2 Modbus Interface
CoolPlug is fully compliant with following Modbus specifications:
·
MODBUS over Serial Line Specification and Implementation Guide V1.02
·
MODBUS application protocol specification V1.1b
CoolPlug supports Modbus RTU Transmission Mode. The default frame format for CoolPlug is:
Baud Rate 9600
Start Bits 1
Data Bits 8
Parity No
Stop Bits 1
CoolPlug physical connection to Modbus is Two-Wire EIA/TIA-485 standard interface via 485-A and 485-B
terminals, recommended by Modbus specification. On such 2W-bus, at any time only one driver has the right for
transmitting thus a Modbus communication is always initiated by the master. CoolPlug will never transmit without
receiving a request from Modbus master.
A number of CoolPlug devices can be connected to single 2W-bus. Each CoolPlug in this case must have
unique Modbus slave address.
Supported Modbus Functions
Function Code
Function Description
03 (0x03)
Read Holding Registers
06 (0x06)
Write Single Register
16 (0x10)
Write Multiple registers
43 14 (0x2B 0x0E) Read Device Information
