PCF85363ATLSLASHA datasheet(23/86 Pages) NXP

23 / 86 page

NXP Semiconductors

PCF85363A

Tiny Real-Time Clock/calendar with 64 byte RAM, alarm function, battery switch-over time stamp input,

and I2C-bus

Remark: Note that all timings are generated from the 32.768 kHz oscillator and are

based on the assumption that there is 0 ppm deviation. Deviation in oscillator frequency

results in deviation in timings. This is not applicable to interface timing.

The WatchDog counts down from a software-loaded 5-bit binary value, WDR[4:0], in

with a non-0 value starts the counter. Values from 1 to 31 are allowed.

aaa-009584

WDR counts

countdown value, WDR

WatchDog clock

counter

WDF

INTA or INTB

duration of first WatchDog period after start

may range from WDR to WDR -1 counts

In this example, it is assumed that the WatchDog flag (WDF) is cleared before the next

WatchDog period expires and that the interrupt output is set to pulsed mode.

Figure 13. WatchDog repeat mode

If a new value of WDR[4:0] is written before the end of the current WatchDog period, then

this value takes immediate effect.

When starting the timer for the first time or when reloading WDR[4:0] before the

end of the current period, the first period has an uncertainty of maximum one count.

The uncertainty is a result of loading the WDR[4:0] from the interface clock which is

asynchronous from the WatchDog source clock. Subsequent WatchDog periods do not

have such variation.

Reading the WatchDog register returns the current value of the WatchDog counter

(see Figure 13) and

not the initial value WDR[4:0]. Since it is not possible to freeze the

WatchDog counter during read back, it is recommended to read the register twice and

check for consistent results.

7.5.1.1 WatchDog repeat mode

In repeat mode, at the end of every WatchDog period, the WatchDog flag (bit WDF in the

Flags register, Section 7.14) is set and the counter automatically reloads and starts the

next WatchDog period. An example is given in Figure 13. The asserted bit WDF can be

used to generate an interrupt. Bit WDF can only be cleared by command.

7.5.1.2 WatchDog single shot mode

In single shot mode, at the end of the countdown period, the WatchDog flag (bit WDF

in the Flags register, Section 7.14) is set and the counter stops with the value 0. The

WatchDog register must be reloaded to start another WatchDog period.

PCF85363A

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 3.1 — 18 June 2021

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