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MCF51QE128 MCU Series Reference Manual, Rev. 3
286 Freescale Semiconductor
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14.3.1 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).
76543210
R
RTIF RTCLKS RTIE RTCPS
W
Reset: 0 0 0 0 0 0 0 0
Figure 14-2. RTC Status and Control Register (RTCSC)
Table 14-2. 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 14-3. Changing the prescaler value clears the prescaler and RTCCNT
counters. Reset clears RTCPS.
Table 14-3. RTC Prescaler Divide-by values
RTCLKS[0]
RTCPS
0 1 2 3 4 5 6 7 8 9 101112 13 14 15
0 Off 2
3
2
5
2
6
2
7
2
8
2
9
2
10
122
2
10 2
4
10
2
5x10
2
10
3
1 Off 2
10
2
11
2
12
2
13
2
14
2
15
2
16
10
3
2x10
3
5x10
3
10
4
2x10
4
5x10
4
10
5
2x10
5