B&R BRCOMP1-0 Anwenderhandbuch Seite 192

B&R COMPACT PLC
8) Hardware Counter 0
The actual value of hardware counter 0 is stored at addresses $2123 and $2124. It is read by using the
"Load Counter 0" function (see point 6).
Because of hardware limitations, the status of the 4 byte counter 0 in the memory range $2100 - $2103
cannot be synchronized with the hardware counter.
The effect only occurs if "Zero Signal Counter 0 as Interrupt Source" is set. By setting the counter
to different preset values during operation, differentiation between real positioning changes, overflows
or new start values can no longer be made.
This is not the case for any of the other operating modes.
Addresses $2123 and $2124 always indicate the pulse remaining until the interrupt.
NOTE: If the counter is read with the preset value, the preset value is not accepted immediately.
The next pulse decrements the old counter state one more time.
Example
3000
2999
5000
4999
:
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Load with preset value (e.g. with 5000)
The next pulse decrements the old counter state
The preset value is accepted
The second pulse decrements starting from the preset value