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Real-Time Clock
28-12
Freescale Semiconductor
28.4.2
Alarm
There are three alarm registers that mirror the three counter registers. An alarm is set by accessing the
real-time clock alarm registers (RTC_ALRM_HM, RTC_ALRM_SEC, and RTC_ALRM_DAY) and
loading the time minus one second that the alarm must generate an interrupt. If the RTC_IER[ALM] bit is
set when the TOD clock value and the alarm value coincide an interrupt occurs one second later. If the
alarm is not disabled and programmed, an alarm reoccurs every 65,536 days. If a single alarm is desired,
the alarm function must be disabled through the RTC_IER register during the alarm interrupt service
routine.
Section 28.5, “Initialization/Application Information,”
for the correct procedure to follow when
changing the alarm or time-of-day (day, hour, minute, or second) registers.
28.4.3
Sampling Timer
The sampling timer supports application software. The sampling timer generates a periodic interrupt with
the frequency specified by RTC_IER[SAM
n
,2HZ]. This timer can be used for digitizer sampling,
keyboard debouncing, or communication polling. The sampling timer operates only if the real-time clock
is enabled and the 1 Hz signal is programmed to clock at 1 Hz. The sample clock (which is equal to SAM7)
is generated by dividing the RTC oscillator frequency by the value programmed into RTC_GOC[31:9],
which is equal to {RTC_GOCU[15:0], RTC_GOCL[15:9]}.
The following table lists example interrupt frequencies of the sampling timer for possible combinations of
RTC oscillator frequency and RTC_GOC values. The following definitions apply:
RTC_OSC = RTC oscillator frequency
RTC_GOC = RTC_GOCU[15:0] + RTC_GOCL[15:0]
SAMPLE_COUNT = RTC_GOCU[15:0] + RTC_GOCL[15:9]
Multiple RTC_IER[SAM
n
,2HZ] bits may be set and the corresponding bits in the RTC_ISR register are
set at the noted frequencies.
Table 28-15. Example Sampling Timer Frequencies
Sampling
Frequency
RTC_OSC = 32 kHz
RTC_GOC = 0x7D00
SAMPLE_COUNT = 0x3E
RTC_OSC = 32.768 kHz
RTC_GOC = 0x8000
SAMPLE_COUNT = 0x40
RTC_OSC = 38.4 kHz
RTC_GOC = 0x9600
SAMPLE_COUNT = 0x4B
RTC_OSC = 48 kHz
RTC_GOC = 0xBB80
SAMPLE_COUNT = 0x5D
SAM7
516.13 Hz
512.00 Hz
512.00 Hz
516.13 Hz
SAM6
258.06 Hz
256.00 Hz
256.00 Hz
258.06 Hz
SAM5
129.03 Hz
128.00 Hz
128.00 Hz
129.03 Hz
SAM4
64.52 Hz
64.00 Hz
64.00 Hz
64.52 Hz
SAM3
32.26Hz
32.00 Hz
32.00 Hz
32.26Hz
SAM2
16.13 Hz
16.00 Hz
16.00 Hz
16.13
SAM1
8.06 Hz
8.00 Hz
8.00 Hz
8.06 Hz
SAM0
4.03 Hz
4.00 Hz
4.00 Hz
4.03 Hz
2HZ
2.02 Hz
2.00 Hz
2.00 Hz
2.02 Hz
Summary of Contents for MCF54455
Page 33: ...xxviii Freescale Semiconductor ...
Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
Page 843: ...Freescale Semiconductor 1 ...
Page 921: ...Revision History A 6 Freescale Semiconductor ...