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Modbus Protocol
Request
Response
*N = quantity of registers
Error
Any other Function Code request will be returned with an error response indicating the
Function Code is not supported, as well as a request for too much data or data at a
register address that is not present.
11.2.2 TCP/IP interface
The Modbus/TCP interface is attached to the TCP/IP stack that is implemented within the
Anatel PAT700 TOC Analyzer, and will listen to all communications that come in on
Modbus/TCP registered port 502.
The Modbus/TCP client uses the standard TCP methods for communicating with the
driver, as established by the BSD socket interface: connect(), send(), receive() and
close(). Only 1 Server connection is allowed at any time. If there is an active connection,
any attempt at any more connections is ignored.
Once a connection has been established, it will be closed after 90 Seconds of inactivity.
Function Code 1 byte 0x03
Starting Address 2 bytes 0x0000 to 0xFFFF
Quantity of Registers 2 bytes 1 to 125 (0x01 to 0x7D)
Function Code 1 byte 0x03
Byte Count 1 byte 2 x N*
Register Values N* x 2 bytes
Function Code 1 byte 0x83
Exception Code 1 byte
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