Ds3231 extremely accurate i, C-integrated rtc/tcxo/crystal, Pin description – Rainbow Electronics DS3231 User Manual
Page 9: Detailed description
DS3231
Extremely Accurate I
2
C-Integrated
RTC/TCXO/Crystal
_____________________________________________________________________
9
Pin Description
PIN
NAME
FUNCTION
1
32kHz
32kHz Output. This open-drain pin requires an external pullup resistor. It may be left open if not used.
2
V
CC
DC Power Pin for Primary Power Supply. This pin should be decoupled using a 0.1µF to 1.0µF capacitor.
If not used, connect to ground.
3
INT/SQW
Active-Low Interrupt or Square-Wave Output. This open-drain pin requires an external pullup resistor. It may be
left open if not used. This multifunction pin is determined by the state of the INTCN bit in the Control Register
(0Eh). When INTCN is set to logic 0, this pin outputs a square wave and its frequency is determined by RS2
and RS1 bits. When INTCN is set to logic 1, then a match between the timekeeping registers and either of the
alarm registers activates the INT/SQW pin (if the alarm is enabled). Because the INTCN bit is set to logic 1
when power is first applied, the pin defaults to an interrupt output with alarms disabled.
4
RST
Acti ve- Low Reset. Thi s p i n i s an op en- d r ai n i np ut/outp ut. It i nd i cates the status of V
C C
r el ati ve to the
V
P F
sp eci fi cati on. As V
C C
fal l s b el ow V
P F
, the RS T p i n i s d r i ven l ow . W hen V
C C
exceed s V
P F
, for t
R S T
, the RS T
p i n i s d r i ven hi g h i m p ed ance. The acti ve- l ow , op en- d r ai n outp ut i s com b i ned w i th a d eb ounced p ushb utton
i np ut functi on. Thi s p i n can b e acti vated b y a p ushb utton r eset r eq uest. It has an i nter nal 50k
Ω nom i nal val ue
p ul l up r esi stor to V
C C
. N o exter nal p ul l up r esi stor s shoul d b e connected . If the cr ystal osci l l ator i s d i sab l ed , the
star tup ti m e of the osci l l ator i s ad d ed to the t
R S T
d el ay.
5–12
N.C.
No Connection. Must be connected to ground.
13
GND
Ground
14
V
BAT
Backup Power-Supply Input. This pin should be decoupled using a 0.1µF to 1.0µF low-leakage capacitor.
If the I
2
C interface is inactive whenever the device is powered by the V
B A T
input, the decoupling capacitor is
not required. If V
B A T
is not used, connect to ground. UL recognized to ensure against reverse charging when
15
SDA
Serial Data Input/Output. This pin is the data input/output for the I
2
C serial interface. This open-drain pin
requires an external pullup resistor.
16
SCL
Serial Clock Input. This pin is the clock input for the I
2
C serial interface and is used to synchronize data
movement on the serial interface.
Detailed Description
The DS3231 is a serial RTC driven by a temperature-
compensated 32kHz crystal oscillator. The TCXO pro-
vides a stable and accurate reference clock, and
maintains the RTC to within ±2 minutes per year accu-
racy from -40°C to +85°C. The TCXO frequency output
is available at the 32kHz pin. The RTC is a low-power
clock/calendar with two programmable time-of-day
alarms and a programmable square-wave output. The
INT/SQW provides either an interrupt signal due to
alarm conditions or a square-wave output. The clock/cal-
endar provides seconds, minutes, hours, day, date,
month, and year information. The date at the end of the
month is automatically adjusted for months with fewer
than 31 days, including corrections for leap year. The
clock operates in either the 24-hour or 12-hour format
with an AM/PM indicator. The internal registers are
accessible though an I
2
C bus interface.
A temperature-compensated voltage reference and
comparator circuit monitors the level of V
CC
to detect
power failures and to automatically switch to the back-
up supply when necessary. The RST pin provides an
external pushbutton function and acts as an indicator
of a power-fail event.