PCF8523_12 Datasheet, PDF (35/75 Pages) NXP Semiconductors – Real-Time Clock (RTC) and calendar

NXP Semiconductors
PCF8523
Real-Time Clock (RTC) and calendar
8.9.1.7 Programmable timer characteristics
Table 40. Programmable timer characteristics
TAQ[2:0] Timer source
TBQ[2:0] clock frequency
Units Minimum
timer-period
(n = 1)
000
4. 096
kHz 244
001
64
Hz 15.625
010
1
Hz 1
011
1_⁄60
111
1_{⁄3 600}
110
100
Hz 1
Hz 1
Units Maximum
timer-period
(n = 255)
s 62.256
ms 3.984
s
255
min 255
hour 255
Units
ms
s
s
min
hour
8.9.2 Timer A
With the bit field TAC[1:0] in register Tmr_CLKOUT_ctrl (0Fh) Timer A can be configured
as a countdown timer (TAC[1:0] = 01) or watchdog timer (TAC[1:0] = 10).
8.9.2.1 Watchdog timer function
The 3 bits TAQ[2:0] in register Tmr_A_freq_ctrl (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
Table 36).
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
Tmr_A_reg (11h) determines the watchdog timer-period.
The watchdog timer counts down from value n in register Tmr_A_reg (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 19). 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 permanentiy active signal. The TAM bit (register Tmr_CLKOUT_ctrl) 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
PCF8523
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 4 — 5 July 2012
© NXP B.V. 2012. All rights reserved.
35 of 74