M-7084 User Manual, Rev. A1.3 7PH-013-A13
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3. Modbus RTU Protocol
The Modbus protocol is developed by Modicon Inc., originally
developed for Modicon controllers. Detailed information can be
found at
http://www.modicon.com/techpubs/toc7.html
. You can also
visit
http://www.modbus.org
to find more valuable information.
The M-7084 modules support the Modbus RTU protocol. The
communication Baud Rates range from 1200bps to 115200bps. The
parity, data bits and stop bits can be set as N81, N82, E81 and O81.
The following Modbus functions are supported.
Function code
Description
01 (0x01)
Read coils
02 (0x02)
Read discrete inputs
03 (0x03)
Read multiple registers
04 (0x04)
Read multiple input registers
05 (0x05)
Write single coil
06 (0x06)
Write single register
15 (0x0F)
Write multiple coils
16 (0x10)
Write multiple registers
If the function specified in the message is not supported, then the
module responds as follows.
Error Response
00
Address
1 Byte
1 to 247
01
Function code
1 Byte
Function code + 0x80
02
Exception code
1 Byte
01
If a CRC mismatch occurs, the module will not respond.