Data Sheet
PT7C4300
Real-time Clock Module (I
2
C Bus)
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Features
•
•
•
Using external 32.768kHz quartz crystal
Supports I
2
C-Bus's high speed mode (400 kHz)
Includes time (Hour/Minute/Second) and calendar
(Year/Month/Date/Day) counter functions (BCD
code)
•
•
•
•
Automatic power-fail detect and switch circuitry of
battery backup
Operating range: 2.0V to 5.5V
Software clock calibration
Ultra-low battery supply current of 1µA
Description
The PT7C4300 serial real-time clock is a low-power
clock/calendar with a programmable square-wave output.
Address and data are transferred serially via a 2-wire
bidirectional bus. The clock/calendar 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 the 24-
hour format indicator.
Table 1 shows the basic functions of PT7C4300. More
Ordering Information
Part Number
PT7C4300W
PT7C4300WE
Package
8-Pin SOIC
Lead free 8-Pin SOIC
details are shown in section: overview of functions.
Table 1.
Basic functions of PT7C4300
Item
Function
Source: Crystal: 32.768kHz
1
Oscillator
Oscillator enable/disable
Oscillator fail detect
12-hour
Time display
24-hour
Century bit
Time count chain enable/disable
3
4
5
6
7
Programmable square wave output (Hz)
Programmable high/low level output
Communicat
ion
Battery backup
Clock calibration
2-wire I
2
C bus
3-wire bus
Burst mode
PT7C4300
√
√
-
-
√
√
√
512Hz
√
√
-
-
√
√
2
Time
PT0222(02/06)
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Ver: 0
Data Sheet
PT7C4300
Real-time Clock Module (I
2
C Bus)
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Function Block
Recommended Layout for Crystal
PT7C4300
PT7C4307
X1
32.768kHz
Crystal
X2
Local Ground plane
Layer 2
Guard Ring
(connect to gound)
Crystal Specifications
Parameter
Nominal Frequency
Series Resistance
Load Capacitance
Symbol
f
O
ESR
C
L
Min
Typ
32.768
12.5
Max
40
Unit
kHz
kΩ
pF
The crystal, traces and crystal input pins should be isolated from RF generating signals.
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Data Sheet
PT7C4300
Real-time Clock Module (I
2
C Bus)
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Pin Configuration
Pin Description
Pin no.
1
Pin
X1
Type
I
Description
Oscillator Circuit Input.
Together with X1, 32.768kHz crystal is connected between them.
Or external clock input.
Oscillator Circuit Output.
Together with X1, 32.768kHz crystal is connected between them.
2
X2
O
3
VBAT
P
Battery Supply Voltage.
4
GND
P
Ground.
Serial Data Input/Output.
SDA is the input/output pin for the 2-wire serial interface. The
SDA pin is open-drain output and requires an external pull-up resistor.
Serial Clock Input.
SCL is used to synchronize data movement on the I
2
C serial interface.
Frequency Test / Output Driver.
Open drain. 512Hz output when Frequency Test is selected.
Output DC level by register selection. Frequency Test is prior.
Supply Voltage.
5
SDA
I/O
6
SCL
I
7
FT/OUT
O
8
VCC
P
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Data Sheet
PT7C4300
Real-time Clock Module (I
2
C Bus)
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Function Description
Overview of Functions
1.
Clock function
CPU can read or write data including the year (last two digits), month, date, day, hour, minute, and second. Any (two-digit) year
that is a multiple of 4 is treated as a leap year and calculated automatically as such until the year 2100.
2.
Interface with CPU
Data is read and written via the I
2
C bus interface using two signal lines: SCL (clock) and SDA (data).
Since the output of the I/O pin SDA is open drain, a pull-up resistor should be used on the circuit board if the CPU output I/O is
also open drain.
The SCL's maximum clock frequency is 400 kHz, which supports the I
2
C bus's high-speed mode.
3.
Oscillator enable/disable
Oscillator and time count chain can be enabled or disabled at the same time by ST bit.
4.
Calibration function
With the calibration bits properly set, accuracy PT7C4300 can be improved to better than ±2 ppm at 25°C.
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Data Sheet
PT7C4300
Real-time Clock Module (I
2
C Bus)
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Registers
1.
Allocation of registers
Register definition
Addr.
(hex)
*1
Function
Bit 7
ST
*2
×
CEB
*3
×
×
×
Y80
OUT
*4
Bit 6
S40
M40
CB
*3
×
×
×
Y40
FT
*5
Bit 5
S20
M20
H20
×
D20
×
*8
Y20
S
*6
Bit 4
S10
M10
H10
×
D10
MO10
Y10
Bit 3
S8
M8
H8
×
D8
MO8
Y8
Bit 2
S4
M4
H4
W4
D4
MO4
Y4
Calibration
*7
Bit 1
S2
M2
H2
W2
D2
MO2
Y2
Bit 0
S1
M1
H1
W1
D1
MO1
Y1
00
01
02
03
04
05
06
07
Seconds (00-59)
Minutes (00-59)
Hours (00-23)
Days of the week (01-07)
Dates (01-31)
Months (01-12)
Years (00-99)
Control
*3
Caution points:
*1. PT7C4300 uses 3 bits for address. That is if write data to 08H, the data will be written to 00H address register.
*2. Stop bit. When this bit is set to 1, oscillator and time count chain are both stopped.
*3. CEB: Century Enable Bit. CB: Century Bit.
*4. Control FT/OUT pin output DC level when 512Hz square wave is disabled.
*5. Frequency Test. 512Hz square wave output is enabled at FT/OUT pin, which is using for frequency test.
*6. Sign Bit. “1” indicates positive calibration; “0”indicates negative calibration.
*7. Using for modifying count frequency. If 20ppm is wanted to slow down the count frequency, 10 (01010) should be loaded.
Calibration will not affect FT/OUT output frequency.
*8. Don’t care.
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