Mitsubishi Electric MELSEC-Q Series User Manual page 34

A double check is an error control system. In this system, cycle data in AnyWire DB A20 transmission is
recognized as valid data if the data matches with the data of the last transmission or is ignored as invalid data if
the data does not match with the last transmission data. A double check ensures reliability of communication.
A double check is classified into a bit double check and word double check.
Double check of bit data
Double check of word data
• Using the "Switch 3" setting, data (bit or word) to be double-checked within the frame can be selected from the
head area of the transmission frame.
• The bit double check is suitable for digital I/O type slave modules, which use information in units of bits. The word
double check is suitable for analog I/O type slave modules, which use information in units of words.
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Transmission cycle
Bit N time (previous)
If the same bit data is verified twice successively,
input and output are performed as a valid data.
Transmission cycle
Word N time (previous)
If the same word data is verified twice successively,
input and output are performed as a valid data.
Transmission cycle
Bit N+1 times (current)
Transmission cycle
Word N+1 times (current)