PCF8523 NXP [NXP Semiconductors], PCF8523 Datasheet - Page 33

• Manufacturer Part Number: PCF8523
• Description: Real-Time Clock (RTC) and calendar
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
PCF8523
Product data sheet
8.9.1.6 Programmable timer characteristics
8.9.2.1 Watchdog timer function
8.9.2 Timer A
Table 38.
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).
The three 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,
Table
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
The interrupt generated by the watchdog timer function of timer A may be generated as
pulsed signal or a permanent 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:
When loading the counter with 0:
TAQ[2:0]
TBQ[2:0]
001
010
011
000
111
110
100
•
•
•
•
•
•
•
If WTAIE = 1, an interrupt will be generated.
If WTAIE = 0, no interrupt will be generated.
The flag WTAF is reset (WTAF = 0),
Interrupt is cleared,
The watchdog timer starts.
The flag WTAF is reset (WTAF = 0),
Interrupt is cleared,
34).
Programmable timer characteristics
Timer source
clock frequency
4.096
64
1
1
1


60
3600
All information provided in this document is subject to legal disclaimers.
Rev. 3 — 30 March 2011
Units
kHz
Hz
Hz
Hz
Hz
244
15.625
1
Minimum
timer-period
(n = 1)
1
1
Figure
18). In that case:
Real-Time Clock (RTC) and calendar
Units
s
ms
s
min
hour
Maximum
timer-period
(n = 255)
62.256
3.984
255
255
255
1

60
Hz or
PCF8523
© NXP B.V. 2011. All rights reserved.
1

3600
Hz (see
Units
ms
s
s
min
hour
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