DS1302 is a real-time clock capable of counting seconds, minutes, hours, date, month, day of the week and year up to 2100. The leap year compensation is made to incorporate internally. The static RAM DS1302 is of 31 Bytes. A simple serial SPI interface makes DS1302 communicate and interact with any microprocessor or microcontroller having an SPI communication interface. There are two forms of time indication i.e. 24 hours format or 12 hours with an indication of AM/PM. It operates on very low power. Retention of data and clock information can only take 1µW at most. Synchronous serial communication is used for connecting this RTC chip with a microprocessor. RST (reset), I/O (data line) and SCLK (serial clock) are the three terminals required for communication with DS1302. Single byte or multiple byte mode are utilized for data transferring to or from clock or RAM.
DS1302 Pinout DiagramDS1302 is available as an 8-pin IC. Its pinout diagram is shown as:
Pin Configuration Details PINS Details 1 (Power Supply- ) This pin is for connecting the primary power source.VCC1 is connected to a source which acts as back up if the primary source is not present or working. DS1302 actually operates on any of the two i.e. VCC1 or VCC2 depending on the magnitude of a higher one. VCC2 acts as a primary power source if VCC2 > VCC1 + 2 . if VCC2 < VCC1 + 2 , VCC1 acts as a power source.
2 (Oscillator Connection-X1) These pins are meant for connecting standard quartz crystal of oscillation frequency 32.768 kHz. For incorporating an external oscillator of value 32.768 kHz, X1 is connected to an oscillator while X2 is kept open/ floating. 3 (Oscillator Connection-X2) 4 (Ground-GND) This pin is for connecting ground 5 ( Reset- RST) This pin is also named as CE. The input at this pin should be high during a read or write. 6 ( Data line-I/O) This is input push-pull-output. It is bi-directional in nature provided communication is occurring through a three-wire SPI interface. 7 ( Synchronizing Clock-SCLK) This pin is for synchronizing data for serial interfacing. 8 (Power Supply- ) This pin is connected to an energy source which can be recharged. This is for systems using trickle charging. Battery back-up is normally connected. Where and How to Use DS1302 RTC Chip?DS1302 has shift register, control logic, oscillator, real-time clock and RAM as the main constituents of timekeeping through SPI serial communication. The block diagram is correspondingly shown as:
DS1302 ExampleA typical application of DS1302 example is shown as:
The crystal oscillator is connected between pin X1 and X2. Power supplies are connected to VCC2 and VCC1. DS1302 actually operates on any of the two i.e. VCC2 and VCC1 depending on the magnitude of a higher one. VCC2 acts as a primary power source if VCC2 > VCC1 + 2 . if VCC2 < VCC1 + 2 , VCC1 acts as a power source.Pin no. 4 is grounded. The serial communication occurs through pins 4, 5 and 6 as shown above.
Each data transfer starts with a command byte. The MSB determines whether writes to DS1302 are possible or not. If this MSB i.e. bit no 7 is 1 writes to DS1302 is enabled and if its logic 0 writes to DS1302 is disabled. 0 zero logic on bit no. 6 determines clock or calendar data while logic shows RAM data. Bit no. 1 to 5 regards data registers to be input or output. Logic 0 at bit 0 I.e. LSB shows wrote operation and logic 1 shows read operation. This is depicted as:
ApplicationsThe applications of DS1302 include incorporated digital clocks/ timers of various modules in our real lives.
Other equivalents ICs of RTC are: DS1307, DS3231, DS3232
DS1302 interfacing with ArduinoIn this section, we will see an example of interfacing RTC chip with Arduino Uno. We will need an external crystal and a lithium battery to use this IC. Instead of purchasing this IC alone, there are many RTC modules available in the market. You can buy a DS1302 RTC module. Picture of module is shown here:
Real-time Chip FeaturesThe operational features of DS1302 are shown as:
Parameters DS1302 Input leakage (µA) 500 I/O leakage (µA) 500 Active supply current- Oscillator enabled (mA) 0.4 Timekeeping current- Oscillator enabled (µA) 0.3-1.0 Stand by current- Oscillator disabled (nA) 100-200 Trickle charge resistors- R1 (kΩ) 2 Trickle charge resistors- R2 (kΩ) 4 Trickle charge resistors- R3 (kΩ) 8 Trickle charge diode voltage drop (V) 0.7 Input capacitance (pF) 10 Input/ output capacitance (pF) 15 Data to CLK setup Vcc=2V (ns) 200 Data to CLK setup Vcc=5V (ns) 50 CLK to data hold Vcc=2V (ns) 280 CLK to data hold Vcc=5V (ns) 70 CLK to data delay Vcc=2V (ns) 800 CLK to data delay Vcc=5V (ns) 200 CLK low time Vcc=2V (ns) 1000 CLK low time Vcc=5V (ns) 250 CLK high time Vcc=2V (ns) 1000 CLK high time Vcc=5V (ns) 250 CLK frequency Vcc=2V (MHz) 0.5 CLK frequency Vcc=5V (MHz) 2 CLK rise and fall Vcc=2V (ns) 2000 CLK rise and fall Vcc=5V (ns) 500 CE to CLK setup Vcc=2V (µs) 4 CE to CLK setup Vcc=5V (µs) 1 CLK to CE hold Vcc=2V (ns) 240 CLK to CE hold Vcc=5V (ns) 60 CE inactive time Vcc=2V (µs) 4 CE inactive time Vcc=5V (µs) 1 CE to I/O high impedance Vcc=2V (ns) 280 CE to I/O high impedance Vcc=5V (ns) 70 SCLK to I/O high impedance Vcc=2V (ns) 280 SCLK to I/O high impedance Vcc=5V (ns) 70 DS1302 DATASHEET DOWNLOADRetroSearch is an open source project built by @garambo | Open a GitHub Issue
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