Clock operation

M41ST87W

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DocID9497 Rev 11

3.7

Full-time 32 kHz square wave output

The M41ST87Y/W offers the user a special 32 kHz square wave function which defaults to

output on the F32k pin (pin 21) as long as VCC

≥ V

SO, and the oscillator is running

(ST bit = '0'). This function is available within one second (typ) of initial power-up and can

only be disabled by setting the 32 kE bit to '0' or the ST bit to '1.' If not used, the F32k pin

should be disconnected and allowed to float.

Note: The F32k pin is an open drain which requires an external pull-up resistor.

3.8

Power-on reset

The M41ST87Y/W continuously monitors VCC. When VCC falls to the power fail detect trip

point, the

RSTpullslow(opendrain)andremainslowonpower-upfort

rec after VCC passes

VPFD(max). The

RSTpinisanopendrainoutputandanappropriatepull-upresistorshould

be chosen to control rise time.

Note: A power-on reset will result in resetting the following control bits to '0': OFIE, AFE,

ABE, SQWE, FT, WDS, BMB0-BMB4, RB0, RB1, TIE1, and TIE2 (see ).

3.9

Reset inputs (

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The M41ST87Y/W provides two independent inputs which can generate an output reset.

The function of these resets is identical to a reset generated by a power cycle. Table 11:

"Reset AC characteristics" and Figure 26: "RSTIN1 and RSTIN2 timing waveforms"

illustrate the AC reset characteristics of this function. Pulses shorter than tR1 and tR2 will not

generate a reset condition.

RSTIN1andRSTIN2areeachinternallypulleduptoV

CC

through a 100 kΩ resistor. Note that

RSTIN1triggersonthefallingedgewhileRSTIN2

triggers on the rising edge.

Note:

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Figure 26:

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RSTIN1

RST

RSTIN2

tR1

trec

Hi-Z

tR2

trec

Hi-Z