M41ST87YMX6 datasheet(30/42 Pages) STMICROELECTRONICS

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M41ST87Y, M41ST87W

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Square Wave Output

The M41ST87Y/W offers the user a programma-

ble square wave function which is output on the

SQW/FT pin. RS3-RS0 bits located in 13h estab-

lish the square wave output frequency. These fre-

quencies are listed in Table 9. Once the selection

of the SQW frequency has been completed, the

SQW/FT pin can be turned on and off under soft-

ware control with the Square Wave Enable Bit

(SQWE) located in Register 0Ah.

The SQW/FT output is programmable as an N-

channel, open drain output driver, or a full-CMOS

output driver. By setting the Square Wave Open

Drain Bit (SQWOD) to a '1,' the output will be con-

figured as an open drain (with IOL as specified in

Table 17., page 37). When SQWOD is set to '0,'

the output will be configured as full-CMOS (sink

and

source

current

specified

Table

17., page 37).

Note: When configured as open drain (SQWOD =

'1'), the SQW/FT pin requires an external pull-up

resistor.

Table 9. Square Wave Output Frequency

Full-time 32kHz Square Wave Output

The M41ST87Y/W offers the user a special 32kHz

square wave function which defaults to output on

the F32k pin (Pin 21) as long as VCC ≥ VSO, 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 32kE

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.

Square Wave Bits

Square Wave

RS3

RS2

RS1

RS0

Frequency

Units

None

–

32.768

kHz

8.192

kHz

4.096

kHz

2.048

kHz

1.024

kHz

512

256

128

008

014

102

111

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