51 MCU Study Notes——13.1DS1302 Real-time Clock Principle

DS1302 Real Time Clock

Chip schematic:

Pin Diagram:

It should be noted that both VCC1 and VCC2 are connected to external capacitors, but the capacity is different. The capacitance value of the normal backup power supply VCC2 is 100 times that of VCC1. This is not difficult to understand. If the power is cut off, VCC2 will be able to provide power for a longer period of time.

VCC1 (main power supply) --------------Filtering function

VCC2 (backup power supply) -------- discharge to provide power when power is off

Connect the X1 and X2 pins to a crystal oscillator to obtain real-time time

Different pins have different functions. We only introduce some special pins here. If you need them, please refer to the official data sheet.

There are 8 registers inside DS1302, which are responsible for seconds, minutes, hours, days, weeks, months, years and a write protection.

We will introduce them in turn, first looking at the schematic diagram:

Register 0:

The "CH" bit in "Bit7" indicates that the clock starts timing, and 1 indicates that the clock stops timing.

"Bit4~Bit6" represents the tens digit of seconds

"Bit0～Bit3" represents the units digit of seconds

Register 1:

"Bit4~Bit6" indicates the tens digit of the minute

"Bit0～Bit3" represents the unit digit of the minute

Register 2:

Bit7:

1: represents the 12-hour system, divided into morning and afternoon

2: represents 24-hour system

Bit5: When the display is in 12-hour format:

0: indicates morning

1: Indicates afternoon

Bit4: Used together with Bit5 to indicate the tens digit of the hour

Register 7:

Bit7: Write protection bit. If it is 1, writing data is prohibited.

The data is stored in the clock chip in the form of "BCD" code. If we want to display the number "59" on the digital tube, we will display "5" and "9" on different digital tubes respectively, because the data inside the microcontroller is in binary form, that is, it is either 0 or 1.

The numbers we display on the computer actually correspond to ASCII code table values.

Timing diagram:

The rising arrow refers to DS1302

Single byte write/read operation timing diagram:

The first byte: indicates which register to read or write by writing.

Second byte: read and write data

Write Operation:

 MCU----》Data----》`I/O` port----`DS1302`

Read Operation:

 `DS1302`----》Data-----》`I/O` port----MCU

Write Operation:

When writing, the data sent by the microcontroller to the I/O port is binary, so it is necessary to detect the level state of the I/O port to determine whether it is low or high.

The write operation is when the SCLK is low and the microcontroller puts the data on the I/O port. When the SCLK rises, the DS1302 reads the data.

void DS1302Write(unsigned int reg,unsigned int data)

{

unsigned char detect;

DS1302RST = 1; //Only high level can trigger

for(detect = 0x01; detect!=0; detect<<=1) // write address

{

if((detect®)!=0)

{

DS1302DAT = 1;

}

else

{

DS1302DAT = 0; //IO status

}

DS1302CK = 1;

delay();

DS1302CK = 0;

delay();

}

for(detect = 0x01; detect!=0; detect<<1) // write address

{

if((detect&data)!=0)

{

DS1302DAT = 1; //IO port status

}

else

{

DS1302DAT = 0;

}

DS1302CK = 1;

delay();

DS1302CK = 0;

delay();

}

}

Read Operation:

The read operation is the microcontroller's judgment of the state of the I/O port. The microcontroller reads the binary data sent by DS1302 to the I/O port, so it is necessary to judge the high and low of the I/O port one by one.

The read operation is when the SCLK is high, the DS1302 puts data on the I/O port. When SCLK is set to low, the microcontroller can read data from the I/O port.

unsigned int DS1302Read(unsigned int addr) // write address only

{

DS1302RST = 1; // Turn on the main switch

unsigned int detect;

unsigned int dat = 0;

for(detect = 0x01; detect!=0; detect<<=1) // write address

{

if((detect&addr)!=0)

{

DS1302DAT = 1;

}

else

{

DS1302DAT = 0;

}

DS1302CK = 1;

delay();

DS1302CK = 0;

delauy();

}

for(detect = 0x01;detect!=0;detect<<=1)

{

if(DS1302DAT!=0)

{

that|=detect;//

}

DS1302CK = 1; //pull high

delay();

DS1302CK = 0; //Pull low to complete a bit transmission

delay();

}

DS1302RST = 0; //The total level is set low to complete the transmission

return dat; // return data

}

Summarize:

MCU read and write operations on DS1302

In fact, it is the microcontroller's judgment of the I/O port status.

Then pull the second bus high and low