Product Specs

Table Of Contents
25 RTC Real-time counter
Page
243
10009.576 µs counter period
2. Desired COUNTER frequency 8 Hz (125 ms counter period)
PRESCALER = round(32.768 kHz / 8 Hz) 1 = 4095
f
RTC
= 8 Hz
125 ms counter period
Table 44: RTC resolution versus overflow
Prescaler
Counter resolution
Overflow
0
30.517 μs
512 seconds
2
8
-1
7812.5 μs
131072 seconds
2
12
-1
125 ms
582.542 hours
25.3 COUNTER register
The COUNTER increments on LFCLK when the internal PRESCALER register (<<PRESC>>) is 0x00.
<<PRESC>> is reloaded from the PRESCALER register. If enabled, the TICK event occurs on each
increment of the COUNTER. The TICK event is disabled by default.
SysClk
LFClk
TICK
PRESC
0x000
<<PRESC>>
0x000
0x000
0x000
0x000
COUNTER
0x000000
0x000001
0x000002
0x000003
Figure 44: Timing diagram - COUNTER_PRESCALER_0
SysClk
LFClk
TICK
PRESC
0x001
<<PRESC>>
0x000
0x001
0x000
0x001
COUNTER
0x000000
0x000001
Figure 45: Timing diagram - COUNTER_PRESCALER_1
25.4 Overflow features
The TRIGOVRFLW task sets the COUNTER value to 0xFFFFF0 to allow SW test of the overflow condition.
OVRFLW occurs when COUNTER overflows from 0xFFFFFF to 0.
Important: The OVRFLW event is disabled by default.
25.5 TICK event
The TICK event enables low power "tick-less" RTOS implementation as it optionally provides a regular
interrupt source for a RTOS without the need to use the ARM
®
SysTick feature.