M41ST87YSS6F datasheet(35/54 Pages) STMICROELECTRONICS

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M41ST87W

Clock operation

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it is again programmed correctly. A READ of the flags register will reset the watchdog flag

(bit D7; register 0Fh) but does not clear the

IRQ/OUTpin.

The watchdog function is automatically disabled upon power-up and the watchdog register

is cleared.

3.6

Square wave output

The M41ST87Y/W offers the user a programmable square wave function which is output

on the SQW/FT pin. RS3-RS0 bits located in 13h establish the square wave output

frequency. These frequencies are listed in Table 10: "Square wave output frequency".

Once the selection of the SQW frequency has been completed, the SQW/FT pin can be

turned on and off under software 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 configured as an open drain (with IOL as specified in Table 19: "DC

characteristics"). When SQWOD is set to '0,' the output will be configured as full-CMOS

(sink and source current as specified in Table 19: "DC characteristics").

Note: When configured as open drain (SQWOD = '1'), the SQW/FT pin requires an external

pull-up resistor.

Table 10: Square wave output frequency

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

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