GE Industrial Solutions WattStation Pedestal EVSE Charger MODBUS Register Mapping Guide - Manual (Page 4)

WattStation TM EV Charger MODBUS Register Guide
4 GE Energy ©2012 GE Company All Rights Reserved
2 MODBUS Communication Overview
2.1 General Overview
MODBUS is an application layer messaging protocol for device communications over different types
of buses or networks. MODBUS communication adopts client and server model. MODBUS Client
initials the MODBUS communication by issuing MODBUS Request and the MODBUS Server processes
the request and sends back the MODBUS Response as shown in Figure 2.1.
MODBUS client/server model.
Figure 2.1
2.1.1
MODBUS Protocol Data Unit (PDU)
MODBUS protocol itself defines a simple protocol data unit ((PPD
DU U)) independent of the underlying
communication layers as shown in Figure 2.2.
MODBUS PDU format.
Figure - 2.2
Field Description
Function Code Tell MODBUS server what kind of action to perform. For some function
code, sub function code is added to define multiple actions.
Data Contains data information
MODBUS PDU field description
Table – 2.1
MODBUS Client MODBUS Server
MODBUS
Request
MODBUS
Response
Function Code Data
MODBUS PDU