GE Industrial Solutions WattStation Pedestal EVSE Charger MODBUS Register Mapping Guide - Manual (Page 5)

WattStation TM EV Charger MODBUS Register Guide
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2.1.2
MODBUS Application Data Unit (ADU)
Based on the underlying communication bus, additional bus related fields are added to the beginning
(and tailor) of the MODBUS PDU to form MODBUS Application Data Unit. Figure 2-3 shows a MODBUS
Serial ADU format. The MODBUS/TCP ADU format will be addressed in section 2.2.
MODBUS RTU ADU format
Figure – 2.3
2.1.3
MODBUS Data Model
MODBUS uses a ‘big-Endian’ representation for addresses and data items. MODBUS data model maps
data into four different kinds of register ranges each of which has distinguishing characteristics as
shown in Table 2.2. Each MODBUS register is a 16 bits field.
Register Type Object Type Type of Access Comments
Coil Single bit Read-Write This data in this type of registers
can be alterable by an application
program.
Discrete Input Single bit Read-Only This type of data can be provided
by an I/O system.
Input Register 16 bits word Read-Only This type of data can be provided
by an I/O system.
Holding Register 16 bits word Read-Write This data in this type of registers
can be alterable by an application
program.
MODBUS data register types
Table – 2.2
Function Code Data Address CRC
MODBUS ADU