Monitoring Timing Of Cpu Module - Mitsubishi Electric MELSEC iQ-R Series User Manual

Monitoring timing of CPU module

The following explains the timing for programmable controller CPU monitoring when the programmable controller CPU
monitoring function is performed.
To monitor the CPU module, C24 reads the monitoring information (device information and CPU module status information)
from the CPU module at the set interval.
Cycle time
1 to 65535 (unit: 100 ms/s/min) can be registered.
Use the following formula as a reference when registering the cycle time.
■When transmitting device data or the programmable controller CPU status
• Cycle time designation > K + SST + PT + DTT
■When transmitting data in conjunction with the modem function
• Cycle time designation > K + SST + PT + DTT + DTTm + MCDT + CDWT
When modem initialization has not been performed, the modem initialization time will be added. (Performing modem
initialization in advance is recommended.)
The items in the formula above is as follows:
• K: 60 ms constant (C24 internal processing time)
• SST (Sequence scan time): Time required for one scan
• PT (Processing time): Processing time for the "Multiple block batch read word unit command 0406"
For 1 point : 10.2 ms
For 480 points: 21.1 ms
For 960 points: 32.6 ms
• DTT (data transmission time) = 1  Transmission rate  Number of bit for one byte during transmission  Number of byte for
send data
Number of bit for one byte portion during transmission = 1 + Data bit count + Parity bit + Stop bit count (parity bit: Yes = 1,
None = 0)
• DTTm (Data transmission delay time by the modem): Depends on the modem specification, line specification, and line
status.
• MCDT (modem connection and disconnection time): Depends on the modem specifications, line specifications, and line
status.
• CDWT (Line disconnection wait time): Wait time for disconnecting line
• Modem initialization time: Depends on the modem specifications.
Since C24 reads the monitoring information (device data, programmable controller CPU status) at the time of
the next END process of the CPU module after the cycle time elapses, make the cycle time as long as
possible.
The following phenomenon may be occurred if the cycle time is short.
• The number of scan of which CPU module scan time gets longer will be increased.
• The processing time for other data communication functions will be increased due to the increase of the
C24 programmable controller CPU monitoring function processing time.
• The load on the target device will be increased.
6 USING THE PROGRAMMABLE CONTROLLER CPU MONITORING FUNCTION
6.2 Programmable Controller CPU Monitoring Function
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