DS3232 View Datasheet(PDF) - Maxim Integrated
Part Name
Description
MFG CO.
'DS3232' PDF : 18 Pages View PDF
Extremely Accurate I2C RTC with
Integrated Crystal and SRAM
Operation
The block diagram shows the main elements of the
DS3232. The eight blocks can be grouped into four
functional groups: TCXO, power control, pushbutton
function, and RTC. Their operations are described sep-
arately in the following sections.
32kHz TCXO
The temperature sensor, oscillator, and control logic
form the TCXO. The controller reads the output of the
on-chip temperature sensor and uses a lookup table to
determine the capacitance required, adds the aging
correction in AGE register, and then sets the capaci-
tance selection registers. New values, including
changes to the AGE register, are loaded only when a
change in the temperature value occurs. The tempera-
ture is read on initial application of VCC and once every
64 seconds (default, see the description for CRATE1
and CRATE0 in the control/status register) afterwards.
Power Control
This function is provided by a temperature-compensat-
ed voltage reference and a comparator circuit that
monitors the VCC level. When VCC is greater than VPF,
the part is powered by VCC. When VCC is less than VPF
but greater than VBAT, the DS3232 is powered by VCC.
If VCC is less than VPF and is less than VBAT, the
device is powered by VBAT. See Table 1.
Table 1. Power Control
SUPPLY CONDITION
VCC < VPF, VCC < VBAT
VCC < VPF, VCC > VBAT
VCC > VPF, VCC < VBAT
VCC > VPF, VCC > VBAT
POWERED BY
VBAT
VCC
VCC
VCC
To preserve the battery, the first time VBAT is applied to
the device, the oscillator does not start up and no tem-
perature conversions take place until VCC exceeds VPF
or until a valid I2C address is written to the part. After
the first time VCC is ramped up, the oscillator starts up
and the VBAT source powers the oscillator during
power-down and keeps the oscillator running. When
the DS3232 switches to VBAT, the oscillator may be dis-
abled by setting the EOSC bit.
Pushbutton Reset Function
The DS3232 provides for a pushbutton switch to be con-
nected to the RST output pin. When the DS3232 is not in
a reset cycle, it continuously monitors the RST signal for a
low going edge. If an edge transition is detected, the
DS3232 debounces the switch by pulling the RST low.
After the internal timer has expired (PBDB), the DS3232
continues to monitor the RST line. If the line is still low, the
DS3232 continuously monitors the line looking for a rising
edge. Upon detecting release, the DS3232 forces the
RST pin low and holds it low for tRST.
The same pin, RST, is used to indicate a power-fail con-
dition. When VCC is lower than VPF, an internal power-
fail signal is generated, which forces the RST pin low.
When VCC returns to a level above VPF, the RST pin is
held low for tREC to allow the power supply to stabilize.
If the oscillator is not running (see the Power Control
section) when VCC is applied, tREC is bypassed and
RST immediately goes high.
Assertion of the RST output, whether by pushbutton or
power-fail detection, does not affect the internal opera-
tion of the DS3232.
Real-Time Clock
With the clock source from the TCXO, the RTC provides
seconds, minutes, hours, day, date, month, and year
information. The date at the end of the month is automati-
cally adjusted for months with fewer than 31 days, includ-
ing corrections for leap year. The clock operates in either
the 24-hour or 12-hour format with an AM/PM indicator.
The clock provides two programmable time-of-day
alarms and a programmable square-wave output. The
INT/SQW pin either generates an interrupt due to alarm
condition or outputs a square-wave signal and the
selection is controlled by the bit INTCN.
SRAM
The DS3232 provides 236 bytes of general-purpose
battery-backed read/write memory. The I2C address
ranges from 14h to 0FFh. The SRAM can be written or
read whenever VCC or VBAT is greater than the mini-
mum operating voltage.
Address Map
Figure 1 shows the address map for the DS3232 time-
keeping registers. During a multibyte access, when the
address pointer reaches the end of the register space
(0FFh), it wraps around to location 00h. On an I2C
START or address pointer incrementing to location 00h,
the current time is transferred to a second set of regis-
ters. The time information is read from these secondary
registers, while the clock may continue to run. This
eliminates the need to reread the registers in case the
main registers update during a read.
I2C Interface
The I2C interface is accessible whenever either VCC or
VBAT is at a valid level. If a microcontroller connected to
the DS3232 resets because of a loss of VCC or other
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