PCF8523TSLASH1 datasheet(36/75 Pages) NXP

36 / 75 page

PCF8523

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Product data sheet

Rev. 4 — 5 July 2012

36 of 74

NXP Semiconductors

PCF8523

Real-Time Clock (RTC) and calendar

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.

8.9.2.2

Countdown timer function

When configured as a countdown timer (TAC[1:0] = 01), timer A counts down from the

software programmed 8-bit binary value n in register Tmr_A_reg (11h). When the counter

reaches 1, the following events occur on the next rising edge of the timer clock (see

Figure 20):

• The countdown timer flag CTAF (register Control_2) is set logic 1

• When the interrupt generation is enabled (CTAIE = 1), an interrupt signal on INT1 is

generated

• The counter automatically reloads

• The next timer-period starts

TAC[1:0] = 10, WTAIE = 1, WTAF = 1, an interrupt is generated.

Fig 19. Watchdog activates an interrupt when timed out

013aaa327

watchdog

timer value

WTAF

n = 0

MCU

INT1

n = 1

PCF8523T/1 数据表(PDF) 36 Page - NXP Semiconductors

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