m41st87w STMicroelectronics, m41st87w Datasheet - Page 30

• Manufacturer Part Number: m41st87w
• Description: 5.0, 3.3, Or 3.0v, 1280 Bit 160 X8 Secure Serial Rtc And Nvram Supervisor With Tamper Detection
• Manufacturer: STMicroelectronics

M41ST87Y, M41ST87W
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
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 F
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
30/42
32k
RS3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
pin (Pin 21) as long as V
RS2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
Square Wave Bits
CC
V
SO
, and the
RS1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
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 I
Table 17., page
the output will be configured as full-CMOS (sink
and source current as specified in
17., page
Note: When configured as open drain (SQWOD =
'1'), the SQW/FT pin requires an external pull-up
resistor.
Bit to '0' or the ST Bit to '1.' If not used, the F
should be disconnected and allowed to float.
Note: The F
an external pull-up resistor.
RS0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
37).
32k
pin is an open drain which requires
37). When SQWOD is set to '0,'
Frequency
32.768
8.192
4.096
2.048
1.024
None
512
256
128
64
32
16
8
4
2
1
Square Wave
OL
as specified in
Units
kHz
kHz
kHz
kHz
kHz
Hz
Hz
Hz
Hz
Hz
Hz
Hz
Hz
Hz
Hz
–
32k
Table
pin