SWCU192 November 2021 CC1312R7 , CC1352P7 , CC2652P7 , CC2652R7
20.4.5.3.4 Pulse Counting
The prescaler can function as a pulse counter when it is not used as event prescaler for TDC start events and stop events.
To initialize the prescaler for the purpose of pulse counting, use the sequence that follows:
- Set AUX_TDC:PRECTL.RESET_N to 0 to reset the prescaler. This resets the internal counter, and clears the AUX_TDC_PRE event. However, the AUX_TDC_PRE event is not used when counting pulses.
- Configure AUX_TDC:PRECTL.SRC to set the prescaler event source.
Set AUX_TDC:PRECTL.RESET_N to 1 to enable the prescaler for pulse counting.
The prescaler now requires three or four event pulses before it starts to count. The number of required pulses is dependent on the timing between reset release and event pulse arrival, as shown in Figure 20-22.
Figure 20-22 Pulse Counting
If the event pulse is inactive at the time of reset release, the counter starts to increment at the fourth event pulse. Hence, the counter value is as follows:
- If number of event pulses is less than 3, counter equals two.
- Otherwise, counter equals number of event pulses minus 1.
The situation becomes different if the user does not control the level of the event at reset release. In this case, the counter may require one more event pulse before it starts to increment. Hence, the counter value could behave as follows:
- If number of event pulses is less than 4, counter equals two.
- Otherwise, counter equals number of event pulses minus 2.
Because of this uncertainty, it is advised to control the level of the selected event at time of reset release.
For information about how to read the prescaler counter value, see AUX_TDC:PRECNTR in Section 20.8.5.