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DEMO9S08DZ60
Chapter 15 Real-Time Counter (S08RTCV1)
MC9S08DZ60 Series Data Sheet, Rev. 4
314
Freescale Semiconductor
15.3.2
RTC Counter Register (RTCCNT)
RTCCNT is the read-only value of the current RTC count of the 8-bit counter.
15.3.3
RTC Modulo Register (RTCMOD)
15.4
Functional Description
The RTC is composed of a main 8-bit up-counter with an 8-bit modulo register, a clock source selector,
and a prescaler block with binary-based and decimal-based selectable values. The module also contains
software selectable interrupt logic.
and a prescaler block with binary-based and decimal-based selectable values. The module also contains
software selectable interrupt logic.
After any MCU reset, the counter is stopped and reset to 0x00, the modulus register is set to 0x00, and the
prescaler is off. The 1-kHz internal oscillator clock is selected as the default clock source. To start the
prescaler, write any value other than zero to the prescaler select bits (RTCPS).
prescaler is off. The 1-kHz internal oscillator clock is selected as the default clock source. To start the
prescaler, write any value other than zero to the prescaler select bits (RTCPS).
Three clock sources are software selectable: the low power oscillator clock (LPO), the external clock
(ERCLK), and the internal clock (IRCLK). The RTC clock select bits (RTCLKS) select the desired clock
source. If a different value is written to RTCLKS, the prescaler and RTCCNT counters are reset to 0x00.
(ERCLK), and the internal clock (IRCLK). The RTC clock select bits (RTCLKS) select the desired clock
source. If a different value is written to RTCLKS, the prescaler and RTCCNT counters are reset to 0x00.
7
6
5
4
3
2
1
0
R
RTCCNT
W
Reset:
0
0
0
0
0
0
0
0
Figure 15-4. RTC Counter Register (RTCCNT)
Table 15-4. RTCCNT Field Descriptions
Field
Description
7:0
RTCCNT
RTC Count. These eight read-only bits contain the current value of the 8-bit counter. Writes have no effect to this
register. Reset, writing to RTCMOD, or writing different values to RTCLKS and RTCPS clear the count to 0x00.
register. Reset, writing to RTCMOD, or writing different values to RTCLKS and RTCPS clear the count to 0x00.
7
6
5
4
3
2
1
0
R
RTCMOD
W
Reset:
0
0
0
0
0
0
0
0
Figure 15-5. RTC Modulo Register (RTCMOD)
Table 15-5. RTCMOD Field Descriptions
Field
Description
7:0
RTCMOD
RTC Modulo. These eight read/write bits contain the modulo value used to reset the count to 0x00 upon a compare
match and set the RTIF status bit. A value of 0x00 sets the RTIF bit on each rising edge of the prescaler output.
Writing to RTCMOD resets the prescaler and the RTCCNT counters to 0x00. Reset sets the modulo to 0x00.
match and set the RTIF status bit. A value of 0x00 sets the RTIF bit on each rising edge of the prescaler output.
Writing to RTCMOD resets the prescaler and the RTCCNT counters to 0x00. Reset sets the modulo to 0x00.