Product Specs

25 RTC — Real-time counter
Page
247
Table 45: RTC jitter magnitudes on tasks
Task
Delay
CLEAR, STOP, START, TRIGOVRFLOW
Table 46: RTC jitter magnitudes on events
+15 to 46 μs
Operation/Function
Jitter
START to COUNTER increment
+/- 15 μs
COMPARE to COMPARE
22
+/- 62.5 ns
1. CLEAR and STOP (and TRIGOVRFLW; not shown) will be delayed as long as it takes for the peripheral
to clock a falling edge and rising of the LFCLK. This is between 15.2585 µs and 45.7755 µs – rounded to
15 µs and 46 µs for the remainder of the section.
SysClk
LFClk
PRESC
COUNTER
CLEARa
CLEARb
Figure 53: Timing diagram - DELAY_CLEAR
SysClk
LFClk
PRESC
COUNTER
STOPa
STOPb
Figure 54: Timing diagram - DELAY_STOP
2. The START task will start the RTC. Assuming that the LFCLK was previously running and stable, the
first increment of COUNTER (and instance of TICK event) will be typically after 30.5 µs +/-15 µs. In
some cases, in particular if the RTC is STARTed before the LFCLK is running, that timing can be up to
~250 µs. The software should therefore wait for the first TICK if it has to make sure the RTC is running.
Sending a TRIGOVRFLW task sets the COUNTER to a value close to overflow. However, since the
update of COUNTER relies on a stable LFCLK, sending this task while LFCLK is not running will start
LFCLK, but the update will then be delayed by the same amount of time of up to ~250 us. The figures
show the smallest and largest delays to on the START task which appears as a +/-15 µs jitter on the first
COUNTER increment.
22
Assumes RTC runs continuously between these events.
Note: 32.768 kHz clock jitter is additional to the numbers provided above.
CLEAR
0x000
X
X+1
0x000000
0x000001
0 or more SysClk after
<= ~46 us
>= ~15 us
1 or more SysClk before
STOP
0x000
X
X+1
0 or more SysClk after
<= ~46 us
>= ~15 us
1 or more SysClk before