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 readin
a re
ister:
00 01 00 00 00 06 01 03 00 00 00 01
This example has the folowin
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. The
include:
Data access
Read/write both discrete and analo
data values from PLC re
ister files.
Online
programming
Services make relativel
minor alterations to ladder lo
ic pro
rams with a hi
hl
controlled introduction of these chan
es into the executin
pro
ram.
Image download/
upload
Ima
e download services support the downloadin
of a ladder lo
ic control
pro
ram to the PLC. Ima
e upload services support the uploadin
of a ladder lo
ic
control pro
ram from a PLC to PC host for archival/backup purposes.
Configuration
Confi
uration services allow the user to define parameter values which affect the
PLC’s re
ister files, I/O map, communication port confi
uration 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 re
uire the user to be in an application lo
in context which is obtained
throu
h other Modbus services.
Modbus Application Protocol PDU
Example
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