M48T201V datasheet(20/35 Pages) STMICROELECTRONICS

20 / 35 page

Clock operation

M48T201Y, M48T201V

20/35

In order to perform a software reset of the watchdog timer, the original time-out period can

be written into the Watchdog Register, effectively restarting the count-down cycle.

Should the watchdog timer time-out, and the WDS Bit is programmed to output an interrupt,

a value of 00h needs to be written to the Watchdog Register in order to clear the IRQ/FT pin.

This will also disable the watchdog function until it is again programmed correctly. A READ

of the Flags Register will reset the Watchdog Flag (Bit D7; Register 7FFF0h).

The watchdog function is automatically disabled upon power-down and the Watchdog

frequency test function is activated, the watchdog or alarm function prevails and the

frequency test function is denied.

Note:

The user must transition the address (or toggle chip enable) to see the Flag Bit change.

3.7

Square wave output

The M48T201Y/V offers the user a programmable square wave function which is output on

the SQW pin. RS3-RS0 Bits located in 7FFF0h establish the square wave output frequency.

These frequencies are listed in Table 7. Once the selection of the SQW frequency has been

completed, the SQW pin can be turned on and off under software control with the Square

Wave Enable Bit (SQWE) located in Register 7FFF6h.

Table 7.

Square wave output frequency

Square Wave Bits

Square wave

RS3RS2

RS1RS0

Frequency

Units

000

Hi-Z

32.768

kHz

001

8.192

kHz

001

4.096

kHz

010

2.048

kHz

010

1.024

kHz

011

512

011

256

100

128

100

101

110

111

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