M41ST85WMH View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

M41ST85WMH

3.0/3.3V I²C combination serial RTC, NVRAM supervisor and microprocessor supervisor

STMicroelectronics 

M41ST85W

Clock operation

IRQ/FT/OUT pin. This will also disable the watchdog function until it is again programmed

correctly. A READ of the Flags Register will reset the Watchdog Flag (Bit D7; Register 0Fh).

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

is cleared. If the watchdog function is set to output to the IRQ/FT/OUT pin and the frequency

test function is activated, the watchdog function prevails and the frequency test function is

denied.

3.6

Square wave output

The M41ST85W 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 4. 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.

Table 4.

Square wave output frequency

Square wave bits

RS3

RS2

RS1

RS0

0

0

0

0

0

0

0

1

0

0

1

0

0

0

1

1

0

1

0

0

0

1

0

1

0

1

1

0

0

1

1

1

1

0

0

0

1

0

0

1

1

0

1

0

1

0

1

1

1

1

0

0

1

1

0

1

1

1

1

0

1

1

1

1

Square wave

Frequency

Units

None

–

32.768

kHz

8.192

kHz

4.096

kHz

2.048

kHz

1.024

kHz

512

Hz

256

Hz

128

Hz

64

Hz

32

Hz

16

Hz

8

Hz

4

Hz

2

Hz

1

Hz

3.7

Power-on reset

The M41ST85W continuously monitors VCC. When VCC falls to the power fail detect trip

point, the RST pulls low (open drain) and remains low on power-up for trec after VCC passes

VPFD(max). The RST pin is an open drain output and an appropriate pull-up resistor should

be chosen to control rise time.

25/41

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