DS3231 查看數據表（PDF） - Dallas Semiconductor -> Maxim Integrated

零件编号

产品描述 (功能)

生产厂家

DS3231

Extremely Accurate I2C-Integrated RTC/TCXO/Crystal

Dallas Semiconductor -> Maxim Integrated 

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

Operation

The block diagram shows the main elements of the

DS3231. 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, or when a

user-initiated temperature conversion is completed.

The temperature is read on initial application of VCC

and once every 64 seconds 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 DS3231 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 will not start up until VCC is

applied, or until a valid I2C address is written to the

part. Typical oscillator startup time is less than one sec-

ond. Approximately 2 seconds after VCC is applied, or

a valid I2C address is written, the device makes a tem-

perature measurement and applies the calculated cor-

rection to the oscillator. Once the oscillator is running, it

continues to run as long as a valid power source is

available (VCC or VBAT), and the device continues to

measure the temperature and correct the oscillator fre-

quency every 64 seconds.

Pushbutton Reset Function

The DS3231 provides for a pushbutton switch to be con-

nected to the RST output pin. When the DS3231 is not in

a reset cycle, it continuously monitors the RST signal for a

low going edge. If an edge transition is detected, the

DS3231 debounces the switch by pulling the RST low.

After the internal timer has expired (PBDB), the DS3231

continues to monitor the RST line. If the line is still low, the

DS3231 continuously monitors the line looking for a rising

edge. Upon detecting release, the DS3231 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 approximately 250ms (tREC) to allow the power sup-

ply 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.

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.

Address Map

Figure 1 shows the address map for the DS3231 time-

keeping registers. During a multibyte access, when the

address pointer reaches the end of the register space

(12h), 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 DS3231 resets because of a loss of VCC or other

event, it is possible that the microcontroller and DS3231

I2C communications could become unsynchronized,

e.g., the microcontroller resets while reading data from

the DS3231. When the microcontroller resets, the

10 ____________________________________________________________________

Share Link: