Datasheet

PCF8523 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 6 — 17 September 2013 36 of 78
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 T_A 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
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