8051 PROGRAMMING IN C

C V.S. Assembly language

Advantage of C Its easier to program in C compared to assembly. C code can be easily ported to other microcontroller, while assembly language can usually be used for 1 type of microcontroller There are lots of function libraries written in C Advantage of assembly language The hex file generated by assembly is usually smaller Code efficiency is higher (faster)

C programming

C has become the standard for embedded system programming Object oriented language (C++, Java, C#) are usually not as efficient as C C is flexible One of the main concerns in C programming for embedded system is to generate a hex file that is small in size We need to pay attention to the size of variables during programming

DATA TYPE Following different Data typesunsigned char (8 bit :- Range 0-255)signed char(8 bit:-Range -128 to +127)unsigned int (16 bit Range= 0 to 65565) signed int, (16 bit Range -32768 to to 32767) sbit, ( 1bit)bit ( 1 bit :-assigned address in bit addressable ram space (20 to 2f)h) sfr ( access special function registers in 51)

Time delay Two methods to achieve time delay: Timer Loop When using loops in C, its difficult to determine the exact time delay by means of calculation For the same C code, different compilers usually will generate different assembly codes Thus the same C codes with different compilers might generate different delays The only way to know the exact delay is through oscilloscope.

Unsigned char 8-bit. Most popular data type, matches most registers. Represent ASCII code or integers in the range of 0 ~ 255. Example: write a C program to send the ASCII code of 0, 1, 2, A, B, C to port 1 #include // the definition of registersvoid main (void){unsigned char mynum[ ]= {1,2,3,'a','b','c'};unsigned char z;for (z = 0; z

signed char An 8-bit number with the most significant bit representing sign (+ or -) Range: -128 ~ 127 Example: write a C program to send -3 to 3 to port 1#include void main(void){char mynum[] = {-3,-2,-1,0,1,2,3}; // signed charunsigned char z;for (z = 0; z

IntegerUnsigned int 16-bit (needs two registers), range: 0 ~ 65535 (FFFFH) E.g.: unsigned int a;Example: write a C program to toggle all bits of P1 continuously #include void main(void){ unsigned int i; P1 = 0x00; // turn off bit for (i =0;i

Signed integerSigned int 16-bit, MSB represents sign. - Range: -32768 ~ 32767 E.g.: int a; Since int requires twice as many memory space as char, use unsigned or signed int only when the number cannot be represented with unsigned or signed char.

Single bit :-sbit Single bit, used to access single-bit addressable registers Example: write a C program to toggle bit D0 of P1 50,000 times#include sbit MYBIT = P1^0;void main(void){unsigned int z;// 50000 times, cannot use charfor (z=0; z

bit Used to access single bit of bit-addressable RAM (20H 2FH) Example: bit mybit = 0; // the compiler will assign a RAM space to automaticallysfr Used to access special function registers example: sfr ACC = 0xE0; // the address of reg. A

Time Delay Two methods to achieve time delay: Loop When using loops in C, its difficult to determine the exact time delay by means of calculationFor the same C code, different compilers usually will generate different assembly codes Thus the same C codes with different compilers might generate different delaysThe only way to know the exact delay is through oscilloscope.

I/O Programming :-Byte size Example: write a program to get a byte of data from P0. If its less than 100,send it to P1; otherwise send it to P2

Bit addressable I/O programmingExample: write a program to monitor bit P1.5. If it is high, send 55H to P0;otherwise send AAH to P2

SFR RegistserExample: read P0, send the result to P1; read in the value of P2.6

Logic operationsLogic operatorsAnd :- &&Or :- ||Not :- ! Example: if (var1 < 3 && var2 == 1)if (!(var > 5))

Bitwise logic operators

- Bit-by-bit logical operations: & (and), | (or), ^ (xor), ~ (not) Shifting: > (shift to right)

Example #include void main(void){P0=0x35 & 0x0F;P1=0x04 | 0x68;P2=0x04 ^ 0x78;P3=~0x55;P0 = 0x35

write a C program to bring in a byte of data serially one bit at a timevia P1.0. LSB should come first #include sbit P1b0 = P1^0;sbin ACCMSB = ACC^7;void main(void){unsigned char x;for (x=0; x> 1;}}

Data Conversion Example: Write a C program to convert packed BCD 0x29 to ASCII, send the result to P1 and P2#include void main(void){unsigned char x, y, z;unsigned char packedBCD = 0x29;x = packedBCD & 0x0F; // extract low nibbleP1 = x | 0x30; // unpacked BCDASCIIx = packedBCD & 0xF0; //extract high nibbley = x>>4; // shift it to low nibbleP2 = y | 0x30; //unpacked BCD ASCII}

Accessing ROM in C To require the compiler store data in ROM, use the code keyword . Without code keyword, all the data will be stored in RAM The compiler will automatically allocate ROM space for the variables. Example#include void main(void){code unsigned char mynum[] = ABCDEF;unsigned char z;for (z = 0; z

Timer program in c Write a program to toggle P1.5 every 250 ms. Use timer 0, mode 2 (8-bit auto reload)#include void T0M2delay25us(void);sbit mybit = P1^5;void main(void){unsigned int x;while(1){mybit = ~mybit;for (x = 0; x < 10000; x++)T0M2delay25us();}}

void T0M2delay25us(void){TMOD = 0x02; // timer 0, mode 2TH0 = -23; // count 23 times,overflow.23*1.085=25 usTR0 = 1; //start timerwhile (TF0 = = 0); //wait till overflow not occursTR0 = 0;TF0=0;}

Timer -counter#include void main( ){T0 = 1; //(make T0 an input)TMOD = 0x05; // 0000 0101 (C/T = 1, mode 1)TL0 = 0;TH0 = 0; //clear counterswhile(1){do{TR0=1; //start timerP1 = TL0;P2 = TH0;}while(TF0 = = 0);TR0 = 0; //stop timerTF0 = 0; //clear TF}}

Assume a 1 Hz external clock is being fed into pin T0 (P3.4). Write a C program for counter T0 in mode 1 (16-bit) to display TH0 and TL0 on P2 and P1, respectively.

Write an 8051 C program to receive a byte of data from serial port 0, then send it back to serial port 0. Do this continuously.

#include void SerTx(unsigned char);void SerRx(unsigned char *);void main(void){char byteBuf;TMOD = 0x20; // timer 1, 8-bit auto-reloadTH1 = 0XFD; // or: TH1 = -3, 9600 baudSCON = 0x50;TR1 = 1; // start timerwhile(1){SerRx(&byteBuf); // read byte from serial portSerTx(byteBuf); // send byte back to serial port}}

void SerTx(unsigned char x){SBUF = x; // put the char in SBUF registerwhile(TI = =0); // wait until transmittedTI = 0;}void SerRx(unsigned char * pX){while(RI = =0); // wait until receivedRI = 0;*pX = SBUF; // copy the data in SBUF to (pX)}