HCS08 datasheet(217/374 Pages) NXP

217 / 374 page

Real-Time Counter (S08RTCV1)

MC9S08JM60 Series Data Sheet, Rev. 5

Freescale Semiconductor

217

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 13-6 shows different prescaler period values.

The RTC modulo register (RTCMOD) allows the compare value to be set to any value from 0x00 to 0xFF.

When the counter is active, the counter increments at the selected rate until the count matches the modulo

value. When these values match, the counter resets to 0x00 and continues counting. The real-time interrupt

flag (RTIF) is set when a match occurs. The flag sets on the transition from the modulo value to 0x00.

Writing to RTCMOD resets the prescaler and the RTCCNT counters to 0x00.

The RTC allows for an interrupt to be generated when RTIF is set. To enable the real-time interrupt, set

the real-time interrupt enable bit (RTIE) in RTCSC. RTIF is cleared by writing a 1 to RTIF.

13.4.1

RTC Operation Example

This section shows an example of the RTC operation as the counter reaches a matching value from the

modulo register.

Table 13-6. Prescaler Period

RTCPS

1-kHz Internal Clock

(RTCLKS = 00)

1-MHz External Clock

(RTCLKS = 01)

32-kHz Internal Clock

(RTCLKS = 10)

32-kHz Internal Clock

(RTCLKS = 11)

0000

Off

0001

8 ms

1.024 ms

250

μs32 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

31.25

μs

31.25 ms

1001

2 ms

62.5

μs62.5 ms

1010

4 ms

5 ms

125

μs

156.25 ms

1011

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

1 s

0.2 s

31.25 ms

6.25 s

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