Schneider Optics Web Embedded Server - Manual (Page 89)

Quantum Ethernet TCP/IP Modbus Application Protocol
840 USE 115 00 Version 1.0 79
Here are the values for a sample mbap_pdu for reading a register:
00 01 00 00 00 06 01 03 00 00 00 01
This example has the folowing structure and content:
inv_id 00 01
proto_id 00 00
len 00 00
dst_idx 01
func_code03
data 00 00 00 01
C.1.2 Modbus Application Protocol Service Classes
There are several classes of service that are part of the Modbus Application
Protocol. They include:
Data access Read/write both discrete and analog data values from PLC register files.
Online
programming Services make relatively minor alterations to ladder logic programs with a highly
controlled introduction of these changes into the executing program.
Image download/
upload Image download services support the downloading of a ladder logic control
program to the PLC. Image upload services support the uploading of a ladder logic
control program from a PLC to PC host for archival/backup purposes.
Configuration Configuration services allow the user to define parameter values which affect the
PLC’s register files, I/O map, communication port configuration and scan attributes,
to name a few.
Device execution
state control The class of service allows the user to start/stop the PLC scan execution. These
services require the user to be in an application login context which is obtained
through other Modbus services.
Modbus Application Protocol PDU Example