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