Real-Time Counter (S08RTCV1)
MC9S08QE128 MCU Series Reference Manual, Rev. 2
242
Freescale Semiconductor
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
2
1
0
R
RTIF
RTCLKS
RTIE
RTCPS
W
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
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 to 0.
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 to 00.
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 to 0.
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
. Changing the prescaler value clears the prescaler and
RTCCNT counters. Reset clears RTCPS to 0000.
Table 13-3. RTC Prescaler Divide-by values
RTCLKS[0]
RTCPS
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0
OFF
2
3
2
5
2
6
2
7
2
8
2
9
2
10
1
2
2
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
OSCOUT
Power On Reset (POR) Default
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