M41T82 datasheet(37/61 Pages) STMICROELECTRONICS

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M41T82-M41T83

Clock operation

Doc ID 12578 Rev 12

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3.8.2

Timer flag (TF)

At the end of a timer countdown, when the timer reloads, TF is set to logic '1.' Regardless of

the state of TF bit (or TI/TP bit), the timer will continue decrementing and reloading.

If both timer and alarm interrupts are used in the application, the source of the interrupt can

be determined by reading the flag bits. Refer to Section 3.14 for more information on the

interaction of these bits. The TF bit is cleared by reading the flags register. This will de-

assert an interrupt output due to the timer.

3.8.3

Timer interrupt enable (TIE, M41T83 only)

In normal interrupt mode (TI/TP = 0), when TF is asserted, the interrupt output is asserted (if

TIE = 1). To de-assert the interrupt, the TF bit or the TIE bit must be reset. Disabling the

interrupt by clearing the TIE bit will de-assert the output, but does not clear the TF bit. Thus,

if TIE is re-enabled prior to clearing TF, the interrupt will assert immediately.

3.8.4

Timer enable (TE)

●

TE = 0

When the timer register (10h) is set to 0, the timer is disabled.

●

TE = 1

The timer is enabled. TE is reset (disabled) on power-down. When re-enabled, the

counter will begin counting from the same value as when it was disabled.

3.8.5

TD1/0

These are the timer source clock frequency selection bits (see Table 12). These bits

determine the source clock for the countdown timer (see Table 10 on page 36). When not in

use, the TD1 and TD0 bits should be set to 11 (1/60 Hz) for power saving.

3.9

Square wave output (M41T83 only)

The M41T83 offers the user a programmable square wave function which is output on the

SQW pin. RS3-RS0 bits located in 13h establish the square wave output frequency. These

frequencies are listed in Table 13. 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 0Ah.

Note:

If the SQWE bit is set to '1' and VCC falls below the switchover (VSO) voltage, the square

wave output will be disabled.

Table 12.

Timer source clock frequency selection (244.1 µs to 4.25 hrs)

TD1

TD0

Timer source clock frequency (Hz)

4096 (244.1 µs)

64 (15.6 ms)

1 (1 s)

1/60 (60 s)

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