UM1539 datasheet(25/46 Pages) STMICROELECTRONICS

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UM1539

Getting started

Doc ID 023106 Rev 1

25/46

1.2.21

M41T82 RTC watchdog configuration

The watchdog of RTC is enabled by configuring the multiplier and resolution settings

and pressing the Write button.

The time period for watchdog is calculated by the resolution x multiplier value. This

value is in seconds.

The watchdog alarm occurs when the time set in the watchdog register has lapsed.

The status of the watchdog alarm can be seen only by pressing the Read Flags button.

Pressing again clears the WDG flag in the alarm register of RTC and its status is shown

in the GUI. The watchdog status on the motherboard (D6 LED) is cleared by writing the

watchdog register. Writing zero disables the watchdog.

1.2.22

M41T82 RTC timer configuration

M41T82 RTC has an 8-bit countdown timer. This timer counts down from the user

configured value to 1 and then again reloads the timer countdown value.

Enter any value between 1 and 255 inside the value bracket of the timer.

Select the timer ticking clock from the clock frequency dropdown menu of the timer.

Enable the checkbox for the TE bit, this enables the timer. If the TE bit is not enabled,

the timer does not start the counting.

Press the Write button to enter the timer configuration values in the timer section of

M41T82 RTC.

As soon as the timer rolls over from 1 to the timer countdown value, the timer flag (TF)

is set inside the flag status register of RTC. This flag is cleared only by reading the flag

1.2.23

M41T82 RTC digital calibration configuration

Enter the calibration value between 0-31 in the calibration register.

Select the positive or negative calibration by selecting the sign in the sign bit dropdown

menu.

Press the Write button to configure the RTC calibration register with the selected

settings.

1.2.24

M41T82 RTC analog calibration configuration

Check the FT bit checkbox.

The slider for analog calibration gets enabled and LED D6 glows on the motherboard.

This disables the remaining RTC window.

Enter the calibration value using the slider and press the Write button to configure the

value inside RTC.

After the value is configured, remove the check from the FT bit checkbox.

1.2.25

M41T82 RTC HT bit configuration

At every power-down, the HT bit is set. To start the display of clock on consecutive

powering, the HT bit should be reset each time.

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