MC9S08DN60 Datasheet, PDF (255/354 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 14 Real-Time Counter (S08RTCV1)
14.4 Functional Description
The RTC is composed of a main 8-bit up-counter with an 8-bit modulo register, a clock source selector,
and a prescaler block with binary-based and decimal-based selectable values. The module also contains
software selectable interrupt logic.
After any MCU reset, the counter is stopped and reset to 0x00, the modulus register is set to 0x00, and the
prescaler is off. The 1-kHz internal oscillator clock is selected as the default clock source. To start the
prescaler, write any value other than zero to the prescaler select bits (RTCPS).
Three clock sources are software selectable: the low power oscillator clock (LPO), the external clock
(ERCLK) and the internal clock (IRCLK). The RTC clock select bits (RTCLKS) are used to select the
desired clock source. If a different value is written to RTCLKS, the prescaler and RTCCNT counters are
reset to 0x00.
RTCPS and the RTCLKS[0] bit select the desired divide-by value. If a different value is written to RTCPS,
the prescaler and RTCCNT counters are reset to 0x00. Table 14-6 shows different prescaler period values.
Table 14-6. Prescaler Period
RTCPS
1-kHz internal clock
source prescaler period
(RTCLKS = 00)
1-MHz external clock
source prescaler period
(RTCLKS = 01)
32-kHz internal clock
source prescaler period
(RTCLKS = 10)
32-kHz internal clock
source prescaler period
(RTCLKS = 11)
0000
Off
Off
Off
Off
0001
8 ms
1.024 ms
250 μs
32 ms
0010
32 ms
2.048 ms
1 ms
64 ms
0011
64 ms
4.096 ms
2 ms
128 ms
0100
128 ms
8.192 ms
4 ms
256 ms
0101
256 ms
16.4 ms
8 ms
512 ms
0110
512 ms
32.8 ms
16 ms
1.024 s
0111
1.024 s
65.5 ms
32 ms
2.048 s
1000
1 ms
1 ms
31.25 μs
31.25 ms
1001
2 ms
2 ms
62.5 μs
62.5 ms
1010
4 ms
5 ms
125 μs
156.25 ms
1011
10 ms
10 ms
312.5 μs
312.5 ms
1100
16 ms
20 ms
0.5 ms
0.625 s
1101
0.1 s
50 ms
3.125 ms
1.5625 s
1110
0.5 s
0.1 s
15.625 ms
3.125 s
1111
1s
0.2 s
31.25 ms
6.25 s
MC9S08DN60 Series Data Sheet, Rev 2
Freescale Semiconductor
255