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IM 04L51B01-01EN
4.1.3 Reading from and Writing to the GX/GP from Other Devices
Other devices (client devices) can transmit commands to the GX/GP to read data from and
write data to the GX/GP internal registers. By writing data to the GX/GP internal registers,
you can control the GX/GP (such as start recording).
For details on the function codes that the GX/GP supports and the GX/GP registers that
client devices can access, see page 4-11 in section 4.5, “Modbus Function and Register
Assignments”.
Specifying Register Numbers
On client devices, specify the GX/GP registers as follows:
• If you are using a commercial SCADA system or something similar, specify the register
number (a number such as 400001; referred to as the “reference number”) listed in
page 4-11 in section 4.5, “Modbus Function and Register Assignments”.
• If you are using a custom communication program, specify the “relative number” in
relation to the reference number. Derive the relative number in the manner indicated in
the examples below.
Examples
The relative number for input register 300100 is 99, which is the difference between
300100 and 300001.
300100 – 300001 = 99
The relative number for input register 400011 is 10, which is the difference between
400011 and 400001.
400011 – 400001 = 10
4.1 Using Modbus/TCP to Enable Other Devices to Read Data from and
Write Data to the GX/GP (Modbus server function)
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