GE Industrial Solutions WattStation Pedestal EVSE Charger MODBUS Register Mapping Guide - Manual (Page 9)

WattStation TM EV Charger MODBUS Register Guide
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3.2 MODBUS Access Control
MODBUS protocol itself does not provide security feature. But in this architecture design, the EVSE
MODBUS communication application module adopts MODBUS access control based on the
MODBUS/TCP client IP address and access privilege. The authorized MODBUS/TCP clients and their
access privileges are set up through EVSE configuration.
Access Privilege MODBUS/TCP
Client IP Address
Read Write
IP Address 1 Bit 0---Data Module 1
.
.
Bit 63---Data Module 64
Value of each bit of
0----read the corresponding
data module is not allowed.
1----read the corresponding
data module is allowed.
Bit 0---Data Module 1
.
.
Bit 63---Data Module 64
Value of each bit of
0----read the corresponding data module
is not allowed.
1----read the corresponding data module
is allowed.
In this version, only Control Command
Module is designed for write.
IP Address 2
IP Address 3
MODBUS Access Control Table
Table – 3.1
EVSE MODBUS/TCP messaging is just over TCP, not over SSL (Secure Socket Layer).
3.3 MODBUS Function Codes Supported
In this architecture design, all data MODBUS can access are mapped into the Holding registers, see
Chapter 20 for detail.
In the following descriptions, the MBAP header is omitted.
In this architecture design, EVSE supports the following function codes:
3.3.1
Function Code 3 (0x03): Read Holding Registers (Multiple)
Function code 0x03 is used to read the contents of a contiguous block of holding registers in EVSE.
The MODBUS Function code 0x03 Request PDU specifies the starting register address and the number
of registers to be read. In the PDU Registers are addressed starting at zero. Therefore registers
numbered 1-16 are addressed as 0-15.