Omron PRT1-COM Operation Manual page 157

Counter Units Section 7-3
Note A priority exists for setting and reading commands. If a bit with a higher priority
always comes first, other settings and readings will not be made, even if they
have been specified. In order of decreasing priority:
1. Count value setting → 2. Set value 2 setting → 3. Set value 1 setting →
4. Count value reading → 5. Set value 2 reading → 6. Set value 1 reading
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