Chapter 6 Communication Mode
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6.4
Modbus slave mode
In modbus slave mode, EH-SIO responds to a query from master according to modbus protocol. Since operation from
receiving a query to sending a response is automatic, no other program is necessary than initial setting.
6.4.1
Overview
EH-SIO gets ready to receive a query after initial setting completed.
When EH-SIO receives a query from external device, EH-SIO analyzes the query and send a command to CPU
module. When EH-SIO receives a response from CPU module, EH-SIO converts the message to Modbus protocol
and send to the external device.
Figure 6.49 Overview of Modbus slave mode
Supported function code
Supported function code and the meanings of EH-SIO are shown below.
Table 6.14 Supported function and meanings
Function
Function
Modbus Original
Corresponding Hitachi PLC I/O
01 (0x01)
Read Coil Status
Read continuous n points of bit output “Y”
02 (0x02)
Read Input Status
Read continuous n points of bit input “X”
03 (0x03)
Read Holding Registers
Read continuous n points of internal register “WR”
04 (0x04)
Read Input Registers
Read continuous n points of internal register “WM”
05 (0x05)
Force Single Coil
Write bit output “Y”
06 (0x06)
Preset Single Register
Write word internal output “WM”
Write word internal output “WR”
*
15 (0x0F)
Force Multiple Coils
Write continuous n point of bit output “Y”
16 (0x10)
Preset Multiple Registers
Write continuous n points of internal register “WR”
* Target internal output of function code 06 can be selected from “WM” and “WR” since software ver. 3.0 or newer.
Master
Command
Query
Response
No user program
Response
Summary of Contents for EH-150 Series
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