Technical information

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Functions (continued)
I/O Scanning service
The I/O Scanning Service is used to manage the exchange of remote I/O states on
the Ethernet network after simple conguration, without the need for any special
programming.
I/O scanning is performed transparently by means of read/write requests according
to the Modbus client/server protocol on the TCP/IP prole.
This principle of scanning via a standard protocol enables communication with any
device supporting Modbus TCP messaging in server mode.
This service can be used to dene:
b A %MW word zone reserved for reading inputs
b A %MW word zone reserved for writing outputs
b Refresh periods independent of the PLC scan
During operation, the module:
b Manages TCP/IP connections with each remote device
b Scans devices and copies the I/O to the congured %MW word zone
b Feeds back status words used to check that the service is working correctly from
the PLC application.
b Applies pre-congured fallback values if a communication error is detected
A range of hardware and software products is available enabling the I/O Scanning
protocol to be implemented on any type of device that can be connected to the
Ethernet network.
Characteristics
b Under Unity Pro software, each station can exchange a maximum of:
v 120 write words
v 125 read words
b Maximum size in the PLC managing the service:
v 1 Kword %MW in inputs and 1 Kword %MW in outputs with manager PLC limited
to 64 stations
v 2 or 4 Kwords %MW in inputs and 2 or 4 Kwords %MW in outputs with manager
PLC limited to 128 stations
I/O Scanning service diagnostics
I/O Scanning service diagnostics can be performed in one of ve ways:
b Via the application program from a specic PLC data zone
b From the setup software debug screen
b From the PLC system diagnostic function displayed by means of an Internet
browser on a PC station
b Using standard SNMP network management software
INPUT
OUTPUT
+
–
INPUT
OUTPUT
+
–
A
B
A
B
Word table
Read Write
Ethernet
Modbus/TCP
Device
input words/
output words
Modicon M580 automation
platform
PlantStruxure Ethernet architectures
Ethernet Modbus/TCP communication services
Functions (continued)
Modicon Premium,
M580 or Quantum
platform with
I/O Scanner
function
(Transparent
Ready class p30)
Device with
Modbus/TCP
messaging in
server mode
2
1
3
4
5
6
7
8
9
10
2
1
3
4
5
6
7
8
9
10