Datasheet

M41ST87Y, M41ST87W Clock operation
Doc ID 9497 Rev 10 37/54
3.6 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 F
32k
pin (pin 21) as long as V
CC
≥ 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 F
32k
pin
should be disconnected and allowed to float.
Note: The F
32k
pin is an open drain which requires an external pull-up resistor.
3.7 Power-on reset
The M41ST87Y/W continuously monitors V
CC
. When V
CC
falls to the power fail detect trip
point, the RST
pulls low (open drain) and remains low on power-up for t
rec
after V
CC
passes
V
PFD
(max). The RST pin is an open drain output and an appropriate pull-up resistor should
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 Table 13 on page 41).
3.8 Reset inputs (RSTIN1 & RSTIN2)
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. Tabl e 10 and
Figure 26 illustrate the AC reset characteristics of this function. Pulses shorter than t
R1
and
t
R2
will not generate a reset condition. RSTIN1 and RSTIN2 are each internally pulled up to
V
CC
through a 100 kΩ resistor. Note that RSTIN1 triggers on the falling edge while RSTIN2
triggers on the rising edge.
Note: RSTIN2
is available only in the SOX28 package.
Figure 26. RSTIN1
& RSTIN2 timing waveforms
AI07072
RSTIN1
RST
RSTIN2
t
R1
t
rec
Hi-Z
t
R2
t
rec
Hi-Z