Omron PRT1-COM Operation Manual page 150

Counter Units
Count Value and External Outputs
140
Counting Range and Underflow/Overflow
The Counter Unit performs counting in the range --8,388,608 to +8,388,607. If
the count value goes outside this range, underflow or overflow will be registered,
and counting will stop.
Note 1. When counting is stopped because of underflow or overflow, it can be
restarted using count value set or reset. For details about count value set or
reset, refer to page 141, Setting and Reading the Count Value and Set
Values.
2. When underflow/overflow occurs, bit 12 in word m+2 of the input area will
come ON. For details, refer to page 144, Word Functions.
3. The Counter Unit will not perform counting until the count mode has been
set. When the Counter Unit is switched ON, however, if the count mode is
already set in word n+2 of the output area, counting will start in the specified
mode.
Set Values 1, 2 and External Outputs
The Counter Unit can set the 2 values, set value 1 and set value 2 , and output
the comparison result, obtained by comparing these values with the count value,
to external outputs 1 and 2. (The comparison result for set value 1 is output to
external output 1 and the comparison result for set value 2 is output to external
output 2.) Output conditions and external output enable/disable can be set
separately for the set values.
Output Conditions:
The following output conditions can be set separately for each of the set values.
Present value ≤ Set value: When the count value is less than or equal to the set
value, the external output will be ON.
Present value ≥ Set value: When the count value is greater than of equal to the
set value, the external output will be ON.
External Output Enable/Disable:
Actual external output will only be made when the External Output Enable Bits
(bits 08 and 09 in word n+2 of the output area) are ON. If the External Output
Enable Bits are OFF, external output will remain OFF, even if the output
conditions are satisfied.
Bit 08 in word n+2: External Output 1 Enable Bit (ON: enable, OFF: disable)
Bit 09 in word n+2: External Output 2 Enable Bit (ON: enable, OFF: disable)
Note 1. Set values 1 and 2, and the output conditions are set in words n, n+1 of the
output area. For details about how to make the settings, refer to the following
Setting and Reading the Count Value and Set Values.
Section 7-3