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MELSEC-QnA
15 FUNCTIONS (FUNCTION VERSION B OR LATER)
15.4 Scan Synchronous Function
This function sets whether link scan is synchronized with the sequence scan, using the
network parameter setting.
15.4.1 Synchronous mode
Performs data link using the scan synchronized with the sequence program. The
operation overview in the synchronous mode is shown in Figure 15.1.
In general, the transmission delay is smaller in the synchronous mode than in the
asynchronous mode.
Select the synchronous mode if the transmission delay is noticeably long.
However, as sequence scan is synchronized with link scan in the synchronous mode,
the link scan is prolonged if the sequence scan is long. In this case, select the
asynchronous mode.
Important
While in the synchronous mode, the scan time must not exceed the time specified for the
corresponding transmission speed, as shown below. If the specified time is exceeded, a time
out error occurs at each station and the station becomes faulty.
Transmission speed Scan time
10Mbps 50ms
5Mbps 50ms
2.5Mbps 100ms
625kbps 400ms
156kbps 800ms
1
Sequence scan > link scan
END END END END
Send
LS : Link scan
SM : Sequence scan
Receive
Send
Send
Send
Output transmission
delay (SM + LS)
Input transmission delay
(SM + LS
2)
ReceiveReceiveReceive
2
Sequence scan < link scan
Output transmission
delay (SM + LS)
END END END END ENDEND END END END
Link scan
Sequence
scan
Input transmission delay
(SM + LS
2)
Send
Send
Send Send
Send
Send
Send
Send
Send
Receive ReceiveReceiveReceive
Figure 15.1 Operation overview in the synchronous mode