Data Sheet
PT7C4302
Real-time Clock Module (3-wire Interface)
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Features
•
•
Using external 32.768kHz quartz crystal
Real-time clock (RTC) counts seconds, minutes
hours, date of the month, month, day of the week,
and year with leap-year compensation valid up to
2099
•
•
•
•
•
•
•
•
•
•
31-byte, nonvolatile (NV) RAM for data storage
2.0V to 5.5V full operation
Uses less than 300nA at 2.0V
Simple 3-wire interface
Serial I/O for minimum pin count
Burst mode for reading/writing successive addresses
in clock/RAM
TTL-compatible (VCC = 5V)
Optional industrial temperature range: -40°C to
+85°C
Battery backup
Trickle charger on chip for rechargeable energy
source backup
Table 1
Basic functions of PT7C4302
Item
Function
Source: Crystal: 32.768kHz
1
Oscillator
Oscillator enable/disable
Oscillator fail detect
Time display
2
Time
12-hour
24-hour
Description
The PT7C4302 serial real-time clock is a low-
power clock/calendar with a programmable square-wave
output and 31 bytes of nonvolatile RAM.
Address and data are transferred serially via a 3-
wire 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 either the 24-hour or
12-hour format with AM/PM indicator.
Table 1 shows the basic functions of PT7C4302.
More details are shown in section: overview of functions.
Ordering Information
Part Number
PT7C4302P
PT7C4302W
Package
8-Pin DIP
8-Pin SOIC
Note:
Lead free package is available by adding “E” after each
part number. For example: PT7C4302PE.
PT7C4302
√
√
-
√
√
-
-
-
√
√
√
-
-
31×8
√
√
3
Communicat
ion
Century bit
Time count chain enable/disable
2-wire I
2
C bus
3-wire bus
Burst mode
Write protection
External clock test mode
Power-on reset override
4
5
6
7
Control
RAM
Charger
Battery backup
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Data Sheet
PT7C4302
Real-time Clock Module (3-wire Interface)
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Function Block
PT7C4302
X1
32.768
kHz
C
D
OSC
Counter
Chain
Time Counter
(Sec,Min,Hour,Day,Date,Month,Year)
31 x 8
RAM
X2
C
G
Address
Decoder
Power Manager
Address
Register
I /O
Interface
(3-wires)
SCLK
RST
I/O
VCC2
VCC1
Shift Registers
Recommended Layout for Crystal
PT7C4302
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
6
Max
45
Unit
kHz
kΩ
pF
The crystal, traces and crystal input pins should be isolated from RF generating signals.
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Data Sheet
PT7C4302
Real-time Clock Module (3-wire Interface)
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Pin Configuration
PT7C4302
1
VCC2
X1
X2
GND
VCC1
SCLK
I/O
RST
8
2
7
3
6
4
5
DIP-8
SOIC-8
Pin Description
Pin no.
1
2
3
Pin
VCC2
X1
X2
Type
P
I
O
Description
Primary power.
When VCC2 is greater than VCC1 + 0.2V, VCC2 will power the PT7C4302.
Oscillator Circuit Input.
Together with X2, 32.768kHz crystal is connected between them.
Oscillator Circuit Output.
Together with X1, 32.768kHz crystal is connected between them.
4
GND
RST
I/O
SCLK
P
Ground.
Reset.
The reset signal must be asserted high during a read or a write. This pin has a 40kΩ
internal pull-down resistor.
Serial Data Input/Output.
I/O is the input/output pin for the 3-wire serial interface. The pin
has a 40kΩ internal pull-down resistor.
Serial Clock Input.
SCLK is used to synchronize data movement on the 3-wire serial
interface. The pin has a 40kΩ internal pull-down resistor.
Backup power.
When VCC2 is less than VCC1, VCC1 will power the PT7C4302. VCC1
provides low-power operation in single supply and battery-operated systems as well as low
power battery backup. In systems using the trickle charger, the rechargeable energy source is
connected to this pin. UL recognized to ensure against reverse charging current when used in
conjunction with a lithium battery.
5
6
7
I
I/O
I
8
VCC1
P
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Data Sheet
PT7C4302
Real-time Clock Module (3-wire Interface)
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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 2099.
2.
Interface with CPU
Simple 3-wire interface.
3.
Oscillator enable/disable
Oscillator can be enabled or disable by /EOSC bit. But time count chain does not shut down when the bit is logic 1.
4.
Charger function
The function is controlled by trickle charge register. Customer can select the charge current by select the number of diode and
resistor value through the register.
For example:
Assume that a system power supply of 5V is applied to VCC2 and a super cap is connected to VCC1. Also assume that the trickle
charger has been enabled with one diode and resistor R1 between VCC2 and VCC1. The maximum current IMAX would,
therefore, be calculated as follows:
IMAX = (5.0V - diode drop)/R1 _ (5.0V - 0.7V) / 2kΩ _ 2.2mA
As the super cap charges, the voltage drop between VCC1 and VCC2 will decrease and, therefore, the charge current will
decrease.
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Data Sheet
PT7C4302
Real-time Clock Module (3-wire Interface)
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Registers
1.
Allocation of registers
Function
Seconds (00-59)
Minutes (00-59)
Hours (00-23 / 01-12)
Dates (01-31)
Months (01-12)
Days of the week (01-07)
Years (00-99)
Control
Trickle charger
Clock burst
*7
RAM
*9
RAM burst
*8
Register definition
Bit 7
/EOSC
*2
0
12, /24
0
0
0
Y80
WP
*3
TCS
*4
-
-
-
Bit 6
S40
M40
0
0
0
0
Y40
0
TCS
-
-
-
Bit 5
S20
M20
H20 or
P /A
D20
0
0
Y20
0
TCS
-
-
-
Bit 4
S10
M10
H10
D10
MO10
0
Y10
0
TCS
-
-
-
Bit 3
S8
M8
H8
D8
MO8
0
Y8
0
DS
*5
-
-
-
Bit 2
S4
M4
H4
D4
MO4
W4
Y4
0
DS
-
-
-
Bit 1
S2
M2
H2
D2
MO2
W2
Y2
0
RS
*6
-
-
-
Bit 0
S1
M1
H1
D1
MO1
W1
Y1
0
RS
-
-
-
Addr.
(hex)
*1
00
01
02
03
04
05
06
07
08
1F
20~3E
3F
Caution points:
*1. PT7C4302 uses 5 bits for address. It’s address byte consists of 1 + RAM/Clock select bit +5-bit addr. + Read/Write select bit.
*2. Oscillator Enable bit. When this bit is set to 1, oscillator is stopped but time count chain is still active.
*3. WP: Write Protect bit. WP bit should be cleared before attempting to write to the device.
*4. TCS: Trickle Charger Select.
*5. DS: Diode Select.
*6. RS: Resistor Select.
*7. Clock burst register address is used as clock/calendar burst mode operation address for consecutively read/write 0~7H
registers. Clock/calendar burst mode operation can continuously read 0H to maximum 7H registers in order; write 0~7H registers
in order. Less or larger than 8 bytes in clock burst write mode are ignored.
*8. RAM burst register address is used as RAM burst mode operation address for consecutively read/write 20~3EH RAM. Less
than 31 bytes in RAM burst read/write mode are valid.
*9. PT7C4302 has 31×8 static RAM for customer use. It is volatile RAM.
*10.
All bits marked with "0" are read-only bits. Their value when read is always "0". All bits marked with "-" are customer
using space.
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