RV-8523 Datasheet, PDF (35/57 Pages) MICORO CRYSTAL SWITZERLAND – Real Time Clock

Micro Crystal
Real Time Clock / Calendar Module
RV-8523
9.9.1.TIMER A
With the bit field TAC[1:0] in register Timer & CLKOUT (0Fh) Timer A can be configured as a countdown timer
(TAC[1:0] = 01) or watchdog timer (TAC[1:0] = 10).
Watchdog timer function:
The three bits TAQ[2:0] in register Timer A Clock (10h) determine one of the five source clock frequencies for the
watchdog timer: 4.096 kHz, 64 Hz, 1 Hz, ¹â„₆₀ Hz or ¹â„₃₆₀₀ Hz (see section 8.6.2.).
The generation of interrupts from the watchdog timer is controlled by using WTAIE bit (register Control 2).
When configured as a watchdog timer (TAC[1:0] = 10), the 8-bit timer value in register Timer A (11h) determines
the watchdog timer-period.
The watchdog timer counts down from value n in register Timer A (11h). When the counter reaches 1, the
watchdog timer flag WTAF (register Control 2) is set logic 1 on the next rising edge of the timer clock (see figure
below). In that case:
• If WTAIE = 1, an interrupt will be generated
• If WTAIE = 0, no interrupt will be generated
The interrupt generated by the watchdog timer function of timer A may be generated as pulsed signal or a
permanently active signal. The TAM bit (register Timer & CLKOUT) is used to control the interrupt generation
mode.
The counter does not automatically reload. When loading the counter with any valid value of n, except 0:
• The flag WTAF is reset (WTAF = 0)
• Interrupt is cleared
• The watchdog timer starts
When loading the counter with 0:
• The flag WTAF is reset (WTAF = 0)
• Interrupt is cleared
• The watchdog timer stops
WTAF is read only. A read of the register Control 2 (01h) automatically resets WTAF (WTAF = 0) and clears the
interrupt.
Watchdog activates an interrupt when timed out:
TAC[1:0] = 10, WTAIE = 1, WTAF = 1, an interrupt is generated.
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