Freescale Semiconductor MPC8313E PowerQUICC II Pro Family Reference Manual page 250

System Configuration
5.5.6 Functional Description
5.5.6.1 Real Time Counter Unit
The real time clock (RTC) timer is suitable for time stamping or time and calendar generation. It can
maintain a one-second count which is unique over a period of approximately 136 years. Software can
convert this count into time-of-day or calendar information if required. An alarm function is also provided.
The RTC can be clocked by the internal system bus clock or by an external clock source. The RTC consists
of 32-bit up-counter which is incremented by an one-second count clock derived from the RTC input clock.
The RTC can be programmed to generate a maskable interrupt when the time value matches the value in
its associated alarm register.
The RTC can be initialized by software with an initial count value in the real time counter load register
(RTLDR). It can also be programmed to generate an interrupt every second. The real time counter control
register (RTCTR) is used to enable or disable the various timer functions. The real time counter event
register (RTEVR) is used to report the interrupt source. The RTC counter is reset to zero on hard reset but
is not affected by soft reset. It is initialized by the software. The RTC function can be disabled.
Figure 5-31 shows the functional RTC block diagram.
RTCNR[CLIN]
RTC
Input
System
Bus Clock
Figure 5-31. Real Time Clock Module Functional Block Diagram
5.5.6.2 RTC Operational Modes
The RTC unit can operate in the following modes:
• RTC enable/disable mode:
RTCNR[CLEN] enables the RTC timer. It should be set by software after a system reset to enable
the RTC timer.
— RTC disable mode (RTCNR[CLEN] = 0)
When the RTC's clock is disabled, counter maintains its old value (default).
— RTC enable mode (RTCNR[CLEN] = 1)
MPC8313E PowerQUICC™ II Pro Integrated Processor Family Reference Manual, Rev. 2
5-42
RTPSR[PRSC]
Clock 32-Bit
Prescaler
Disable
RTCNR[CLEN]
RTCNR[PIM]
RTLDR[CLDV]
RTEVR[PIF]
32-Bit
Counter
RTCTR[CNTV]
=
RTEVR[AIF]
RTCNR[AIM]
RTALR[ALRM]
Second
Interrupt
Alarm
Interrupt
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