Chapter 1
Introduction
RUGGEDCOM RSG2488
User Guide
12
ModBus Management Support
Section 1.6
ModBus Management Support
Modbus management support in RuggedCom devices provides a simple interface for retrieving basic status
information. ModBus support simplifies the job of SCADA (Supervisory Control and Data Acquisition) system
integrators by providing familiar protocols for retrieving RuggedCom device information. ModBus provides mostly
read-only status information, but there are some writable registers for operator commands.
The ModBus protocol PDU (Protocol Data Unit) format is as follows:
Function Code
Data
The following sections describe the support for ModBus management:
•
Section 1.6.1, “ModBus Function Codes”
•
Section 1.6.2, “ModBus Memory Map”
•
Section 1.6.3, “ModBus Memory Formats”
Section 1.6.1
ModBus Function Codes
RuggedCom devices support the following ModBus function codes for device management through ModBus:
NOTE
While RuggedCom devices have a variable number of ports, not all registers and bits apply to all
products.
Registers that are not applicable to a particular device return a zero (0) value. For example, registers
referring to serial ports are not applicable to RuggedSwitch® devices.
Read Input Registers or Read Holding Registers — 0x04 or 0x03
Example PDU Request
Function Code
1 Byte
0x04(0x03)
Starting Address
2 Bytes
0x0000 to 0xFFFF (Hexadecimal)
128 to 65535 (Decimal)
Number of Input Registers
2 Bytes
Bytes 0x0001 to 0x007D
Example PDU Response
Function Code
1 Byte
0x04(0x03)
Byte Count
1 Byte
2 x
N
a
Number of Input Registers
N
a
x 2 Bytes
a
The number of input registers
Write Multiple Registers — 0x10
Example PDU Request
Function Code
1 Byte
0x10
