MC9S08JM16 Datasheet, PDF (213/386 Pages) Freescale Semiconductor, Inc – Microcontrollers

Real-Time Counter (S08RTCV1)
13.3.1 RTC Status and Control Register (RTCSC)
RTCSC contains the real-time interrupt status flag (RTIF), the clock select bits (RTCLKS), the real-time
interrupt enable bit (RTIE), and the prescaler select bits (RTCPS).
7
6
5
4
3
R
RTIF
W
RTCLKS
RTIE
2
1
0
RTCPS
Reset:
0
0
0
0
0
0
0
0
Figure 13-3. RTC Status and Control Register (RTCSC)
Table 13-2. RTCSC Field Descriptions
Field
7
RTIF
6–5
RTCLKS
4
RTIE
3–0
RTCPS
Description
Real-Time Interrupt Flag This status bit indicates the RTC counter register reached the value in the RTC modulo
register. Writing a logic 0 has no effect. Writing a logic 1 clears the bit and the real-time interrupt request. Reset
clears RTIF.
0 RTC counter has not reached the value in the RTC modulo register.
1 RTC counter has reached the value in the RTC modulo register.
Real-Time Clock Source Select. These two read/write bits select the clock source input to the RTC prescaler.
Changing the clock source clears the prescaler and RTCCNT counters. When selecting a clock source, ensure
that the clock source is properly enabled (if applicable) to ensure correct operation of the RTC. Reset clears
RTCLKS.
00 Real-time clock source is the 1 kHz low power oscillator (LPO)
01 Real-time clock source is the external clock (ERCLK)
1x Real-time clock source is the internal clock (IRCLK)
Real-Time Interrupt Enable. This read/write bit enables real-time interrupts. If RTIE is set, then an interrupt is
generated when RTIF is set. Reset clears RTIE.
0 Real-time interrupt requests are disabled. Use software polling.
1 Real-time interrupt requests are enabled.
Real-Time Clock Prescaler Select. These four read/write bits select binary-based or decimal-based divide-by
values for the clock source. See Table 13-3. Changing the prescaler value clears the prescaler and RTCCNT
counters. Reset clears RTCPS.
Table 13-3. RTC Prescaler Divide-by values
RTCPS
RTCLKS[0]
01
2
3
45678
9
10 11 12 13 14 15
0
Off 2³ 2⁵ 2⁶ 2⁷ 2⁸ 2⁹ 2¹⁰ 1
2
2² 10 2⁴ 10² 5x10² 10³
1
Off 2¹⁰ 2¹¹ 2¹² 2¹³ 2¹⁴ 2¹⁵ 2¹⁶ 10³ 2x10³ 5x10³ 10⁴ 2x10⁴ 5x10⁴ 10⁵ 2x10⁵
MC9S08JM16 Series Data Sheet, Rev. 2
Freescale Semiconductor
213