This is not difficult. It's all over the internet. The calendar chip can choose DS 1302, and it won't cost a few dollars. It won't cost a few oceans to choose STC series for single chip microcomputer.

The principle is super simple, Baidu is OK.

Give you a reference program.

I hope it helps you.

Voids 1302 _ limit(void)// initialization

{

ds 1302 _ write enable()；

ds 1302 _ OSC enable()；

for(ds 1302 _ b = 0； ds 1302 _ b & lt； 7; ds 1302_b++)

ds 1302 _ SendByte(ds _ sec+2 * ds 1302 _ b，d 1302[ds 1302 _ b])； //Assignment initialization

}

Uchar ds 1302 _ read (uchar address)//read clock

{

uchar dat

ds 1302 _ write enable()；

Switch (address)

{ case 0:dat = ds 1302 _ receive byte(ds _ sec+ 1)；

Break;

case 1:dat = ds 1302 _ receive byte(ds _ min+ 1)；

Break;

Case 2: DAT = ds1302 _ receivebyte (ds _ hour+1);

Break;

Case 3: DAT = DS1302 _ RECEIVE Byte (DS _ DAY+1);

Break;

Case 4: DAT = DS1302 _ receivebyte (DS _ week+1);

Break;

Case 5: DAT = DS1302 _ receivebyte (DS _ month+1);

Break;

Case 6: dat = ds1302 _ receivebyte (ds _ year+1);

Break;

}

ds 1302 _ write disable()；

return(dat)；

}

Voids1302 _ write (uchar address, uchar dat)

{

ds 1302 _ write enable()；

Switch (address)

{

Case 0: ds1302 _ send byte (ds _ sec, dat);

Break;

Case1:ds1302 _ sendbyte (ds _ min, dat);

Break;

Case 2: DS 1302_SendByte(ds_hour, dat);

Break;

Case 3: DS 1302_SendByte(ds_day, dat);

Break;

Case 4: DS 1302_SendByte(ds_week, dat);

Break;

Case 5: ds1302 _ send byte (ds _ month, dat);

Break;

Case 6: DS 1302_SendByte(ds_year, dat);

Break;

}

ds 1302 _ write disable()；

}

Ds 1302pro() // reading data

{

nian 0 1 = ds 1302 _ receive byte(ds _ year+ 1)；

yue 0 1 = ds 1302 _ receive byte(ds _ month+ 1)；

ri 0 1 = ds 1302 _ receive byte(ds _ day+ 1)；

Xiaoshi 0 1 = ds 1302 _ receive byte(ds _ hour+ 1)；

sec 0 1 = ds 1302 _ receive byte(ds _ sec+ 1)； //Countdown information

min 0 1 = ds 1302 _ receive byte(ds _ min+ 1)； //Read information

Stephen Chow = ds1302 _ receivebyte (ds _ week+1);

d 1302 _ transfer()； //Numerical processing extracts the value to be displayed.

}

Voids 1302 _ send byte (uchar command, uchar xmtdat)// data sending program, which sends 1 byte to the controlled ds1302.

{

Ucal I;

RST = 0；

_ nop _()；

SCLK = 0；

_ nop _()；

RST = 1；

for(I = 0； I<8; i++)

{

IO_DATA= (bit) (command & amp0x01);

Command = Command & gt& gt 1;

SCLK = 1；

_ nop _()；

SCLK = 0；

}

for(I = 0； I<8; i++)

{

IO_DATA= (bit) (xmtdat & amp0x01);

XmtDat = XmtDat & gt& gt 1;

SCLK = 1；

_ nop _()；

SCLK = 0；

}

RST = 0；

}

Uchards1302 _ receivebyte (uchar command)//data receiver; Receive 1 byte data from the controlled DS 1302.

{

uchar i，rcv dat = 0；

RST = 0；

_ nop _()；

SCLK = 0；

_ nop _()；

RST = 1；

for(I = 0； I<8; i++)

{

IO_DATA= (bit) (command & amp0x01);

Command = Command & gt& gt 1;

SCLK = 1；

_ nop _()；

SCLK = 0；

}

for(I = 0； I<7; i++)

{

if(IO _ DATA)rcv dat | = 0x 80；

RcvDat = RcvDat & gt& gt 1;

SCLK = 1；

_ nop _()；

SCLK = 0；

}

if(IO _ DATA)rcv dat | = 0x 80；

RST = 0；

Return to RcvDat

}

Voids1302 _ write enable (void)//allows data to be written into the register.

{

DS 1302_SendByte(ds_com，00)；

}

Voids1302 _ write disable (void)//prohibit data from being written into the register.

{

DS 1302_SendByte(ds_com，0x 80)；

}

Voids1302 _ oscenable (void)//Start clock operation.

{

DS 1302_SendByte(ds_sec，0x 00)；

}

Voids1302 _ OSC disable (void)//Stop the clock operation.

{

DS 1302_SendByte(ds_sec，0x 80)；

}

Void d d1302 _ transfer (void)//data conversion function

{

Year 02 = year 01&; 0x0f

nian 0 1 = nian 0 1 & gt； & gt4;

Yue 02 = Yue 01& 0x0f

yue 0 1 = yue 0 1 & gt； & gt4;

ri02 = ri 0 1 & amp； 0x0f

ri 0 1 = ri 0 1 & gt； & gt4;

Xiaoshi 02 = Xiaoshi 0 1 & amp； 0x0f

Xiaoshi 1 = Xiaoshi 1 & gt； & gt4;

min 02 = min 0 1 & amp； 0x0f

min 0 1 = min 0 1 & gt； & gt4;

sec 02 = sec 0 1 & amp； 0x0f// Take the lower four bits of the Miao language signal.

sec 0 1 = sec 0 1 & gt； & gt4; //Take four high digits.

}

Void delay 1302(int i) // delay function

{

uchar x，j；

for(x = 0； X< me; x++)

{

for(j = 0； j & lt 125; j++){； }

}

}