Sequence Scan Synchronization Specification - Mitsubishi Electric MELSEC iQ-R Series User Manual

Sequence scan synchronization specification

Whether to synchronize the link scan with the sequence scan of a CPU module or not can be selected.
Difference between asynchronous and synchronous settings
■Asynchronous setting
Link scan is performed asynchronously with the sequence scan of the CPU module. Select this item to shorten input
transmission delay time when sequence scan takes much more time than link scan. Note that output transmission delay time
will become longer.
■Synchronous setting
Data link is performed with a scan synchronizing a program. (The sequence scan and link scan start simultaneously.)
Select this item to shorten output transmission delay time. Note, however, that the input transmission delay time becomes
longer if a sequence scan takes much longer than a link scan.
Because of the synchronization, extended sequence scan time increases link scan time.
When a link scan is synchronized with a sequence scan, the L RUN LED may turn on dimly.
Setting method
Set sequence scan synchronization under "Supplementary Cyclic Settings" in "Application Settings". ( Page 69
Supplementary Cyclic Settings)
Data flow
Data flows in the asynchronous mode and synchronous mode are explained below using examples of communications
between a master station and remote I/O station.
■Data flow asynchronous with a sequence scan
CPU module
(sequence scan)
Master station buffer memory
(remote input (RX))
Link scan
Response time of the first station
Response time of the corresponding station
Response time of the final station
Responses from remote
I/O stations
 Delay time due to response delay of the remote I/O station
 Delay time of transmission from the remote I/O station to the master station
 Delay time between the master station receiving data and the data being stored into the buffer memory
 Delay time until information of the master station is refreshed in the CPU module
Input 1 Input 2 Input 3
Ò Ó Ô
Transmission delay time
Õ
1.1 Cyclic Transmission
1
1 FUNCTIONS
31