AN974 Datasheet, PDF (4/6 Pages) STMicroelectronics – Real time clock with ST7 Timer Output Compare

Real time clock with ST7 Timer Output Compare
3.1 HARDWARE CONFIGURATION
The real time clock application hardware is made of a ST72324 microcontroller timer which
generates a 100ms time base through the Timer B Output Compare 1 function . Two of the
software counters (seconds and minutes) are output by the microcontoller through I/O ports
(PC, PF and PD) and displayed on LEDs as shown in Figure 3. The Seconds counter is shown
with a red LED and the Minutes counter is shown with a pink LED.
The selected crystal for this example has 8 MHz frequency which gives f_CPU=4 MHz because
the PLL is disabled and slow mode is not selected.
Figure 3. Real Time Clock Application
PC_2-7
LED
TIMER
OC registers
I/O
PORTS
PF_0,1,4,6,7
PD0
LED
LED
SOFTWARE
ST72324
RAM
sw counter
The RTC accuracy depends on the clock source (e.g. Resonator Oscillator) accuracy. Care
should be taken especially for time critical applications.
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