Chapter 13 Real-Time Counter (S08RTCV1)
MC9S08SG32 Data Sheet, Rev. 7
Freescale Semiconductor
197
13.3.1
RTC Status and Control Register (RTCSC)
RTCSC contains the real-time interrupt status ag (RTIF), the clock select bits (RTCLKS), the real-time
interrupt enable bit (RTIE), and the prescaler select bits (RTCPS).
7
654
3
210
R
RTIF
RTCLKS
RTIE
RTCPS
W
Reset:
0
Figure 13-3. RTC Status and Control Register (RTCSC)
Table 13-2. RTCSC Field Descriptions
Field
Description
7
RTIF
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.
6–5
RTCLKS
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)
4
RTIE
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.
3–0
RTCPS
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
RTCLKS[0]
RTCPS
0
1
2
3
4
5678
9
10
11
12
13
14
15
0
Off
23
25
26
27
28
29
210
12
22
10
24
102
5x102
103
1
Off
210
211
212
213
214
215
216
103
2x103 5x103
104
2x104 5x104
105
2x105