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PT7C4302P

Real-time Clock Module (3-wire Interface)

Pericom Semiconductor Corporation 

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.

PT0225(11/05)

4

Ver: 0

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