PCA8565 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 4 — 5 December 2014 16 of 48
NXP Semiconductors
PCA8565
Real time clock/calendar
[1] Default value.
[2] These bits determine the source clock for the countdown timer; when not in use, TD[1:0] should be set to
1
⁄
60
Hz for power saving.
8.7.2 Register Countdown_Timer
The timer register is an 8-bit binary countdown timer. It is enabled or disabled via the
Timer_control register. The source clock for the timer is also selected by the Timer_control
register. Other timer properties such as single or periodic interrupt generation are
controlled via the register Control_status_2 (address 01h).
For accurate read back of the count down value, it is recommended to read the register
twice and check for consistent results, since it is not possible to freeze the countdown
timer counter during read back.
8.8 Register CLKOUT_control and clock output
A programmable square wave is available at pin CLKOUT. Operation is controlled by the
CLKOUT_control register at address 0Dh. Frequencies of 32.768 kHz (default),
1.024 kHz, 32 Hz and 1 Hz can be generated for use as a system clock, microcontroller
clock, input to a charge pump, or for calibration of the oscillator. CLKOUT is an open-drain
output and enabled at power-on. If disabled it becomes high-impedance.
Table 23. Register Timer_control (address 0Eh) bits description
Bit Symbol Value Description
7TE 0
[1]
timer is disabled
1 timer is enabled
6 to 2 - - unused
1 to 0 TD[1:0] timer source clock frequency select
[2]
00 4.096 kHz
01 64 Hz
10 1 Hz
11
[2] 1
⁄
60
Hz
Table 24. Timer (address 0Fh) bits description
Bit Symbol Value Description
7 to 0 COUNTDOWN_TIMER 00h to FFh countdown period in seconds:
where n is the countdown value
Table 25. Timer register bits value range
Bit
7 6 5 4 3 2 1 0
1286432168421
CountdownPeriod
n
SourceClockFrequency
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