Double Check - Mitsubishi Electric FX3U-128ASL-M User Manual

FX -128ASL-M User's Manual
3U
2.4.2

Double check

The 128ASL-M performs double check as the error control method.
By double check, the 128ASL-M does not update the data in the input area until it receives the same input
data twice consecutively so that noise errors and other transmission errors can be avoided.
Accordingly, data is updated as described below.
1) Input
In the best case, one transmission cycle time and in the worst case, two transmission cycle times are
required as the input data response time to sample once.
Thus, signals of two transmission cycle times or less may not be sampled twice depending on the timing.
Therefore, to ensure response, provide an input signal that is longer than two transmission cycle times.
Single sample
best case
response time
Single sample
worst case
response time
2) Output
As double check is performed on the output slave module side, the time required to sample once is the
same as that for input, namely one transmission cycle time in the best case and two transmission cycle
times in the worst case.
Thus, signals of two transmission cycle times or less may not be sampled twice depending on the timing.
Therefore, to ensure response, provide an input signal that is longer than two transmission cycle times.
20
Sampling timing
Minimum one transmission
cycle time
Input data change
Sampling timing
Maximum two transmission
cycle times
Input data change
2.4 Communication Specifications
Sampling timing
Input data update
Sampling timing
2 Specification
Sampling timing
Input data update