How To Use The Scan Counter - YASKAWA MP210 Series User Manual

Appendix F MP2100M Slave CPU Synchronization Function
F.3.4 How to Use the Scan Counter
F.3.4 How to Use the Scan Counter
Using the scan counter makes it possible to check at the receiving side that data has been refreshed at the trans-
mitting side.
It can also be used to check from the master device that the slave devices are operating normally, or to check
from a slave device that the master device is operating normally.
Since using the scan counter is optional, there is no problem with not using it if it is not necessary.
An example of its use is shown below. In this example it is assumed that the high-speed scan cycle at the master
device and the high-speed scan cycle at the slave devices are the same.
(1) When Checking the Operation Status of the Master Device with the Application at a
Slave Device
Refreshed by the
application every scan
• Processing at master device
The application at the master device increments the value set for the first word of the output registers allo-
cated to the Built-in SVB Module of the MP2100M by 1.
• Processing at slave device
The application at the slave device checks that the scan counter value has increased by 1 compared to the pre-
vious value. Since the scan counter is 1-byte data, it is only the least significant byte that is checked.
If the data has not been refreshed correctly, it is judged that there is a problem with operation at the master
device.
F-18
Master device
Output registers
Scan
OW
counter
OW +1
Slave device
Input registers
Scan
IW
counter
IW +1
Checks that the data has been
refreshed. If it has not been
refreshed correctly, there is
judged to be an operation error
at the master device.