Intel 8051 Programming in C

8051 PROGRAMMING IN C
5th-12th February 2018 & 26th February 2018
Sudhanshu Janwadkar, TA, SV National Institute of Technology, Sura

Why write program in C?
 It is easier and less time consuming to write
codes in C than Assembly
 C is easier to modify and update
 You can use code available in function
libraries
 C code is portable to other microcontroller with
little of no modification

The downside of writing in C
 Compilers produce hex files that is
downloaded to ROM of microcontroller.
 Microcontrollers have limited on-chip ROM
 The size of hex file is the main concern
 C Codes produce a larger hex file.

What is Embedded C?
 Embedded C is a set of language extensions for
the C programming language, enhanced for
different embedded systems.
 The extensions are required to support exotic
features such as fixed-point arithmetic, multiple
distinct memory banks and basic I/O operations.
 Embedded C uses most of the syntax and
semantics of standard C, e.g., main() function,
variable definition, datatype declaration,
conditional statements (if, switch case), loops
(while, for), functions, arrays and strings,
structures and union, bit operations, macros, etc.

unsigned char
 Unsigned char is an 8-bit data type in the range of
0 – 255 (00 – FFH)
 The character data type is the most natural
choice because 8051 is an 8-bit
microcontroller
 Used for
 Counter value
 ASCII characters
 C compilers use the signed char as the default if
we do not put the keyword unsigned

signed char
 The signed char is an 8-bit data type
 Use the MSB D7 to represent – or +
 Give us values from –128 to +127
 We should stick with the unsigned char unless
the data needs to be represented as signed
numbers

unsigned int
 The unsigned int is a 16-bit data type
 Takes a value in the range of 0 to 65535 (0000 –
FFFFH)
 Used for:
 Define 16-bit variables such as memory
addresses
 Set counter values of more than 256
 Since registers and memory accesses are in 8-bit
chunks, the misuse of int variables will result in a
larger hex file

signed int
 Signed int is a 16-bit data type
 Use the MSB D15 to represent – or +
 We have 15 bits for the magnitude of the
number from –32768 to +32767

bit, sbit and sfr
 The bit data type allows access to single bits
of bit-addressable memory spaces 20 – 2FH
 To access bits of SFRs, we use sbit data type.
 To access the byte-size SFR registers, we use
the sfr data type

Write an 8051 C program to send values 00 – FF
to port P1.
#include <reg51.h>
void main(void)
{
unsigned char i;
for (i=0;i<=255;i++)
P1=i;
}

Write an 8051 C program to send hex values for
ASCII characters of 0, 1, 2, 3, 4, 5, A, B, C, and D
to port P1.
#include <reg51.h>
void main(void)
{
unsigned char mynum[]=“012345ABCD”;
unsigned char i;
for (i=0;i<=10;i++)
P1=mynum[i];
}
 Note:
1. Pay careful attention to the size of the data
2. Try to use unsigned char instead of int, whenever

Write an 8051 C program to toggle all the bits of
P1 continuously.
#include <reg51.h>
void main(void)
{
While (1)
{
p1=0x55;
p1=0xAA;
}
}

Write an 8051 C program to send values of –4 to
+4 to port P1.
//Singed numbers
#include <reg51.h>
void main(void)
{
char mynum[]={+1,-1,+2,-2,+3,-3,+4,-4};
unsigned char i;
for (i=0;i<=8;i++)
P1=mynum[i];
}

Write an 8051 C program to send values of –4 to
+4 to port P1.
//Singed numbers
#include <reg51.h>
void main(void)
{
signed char i;
for (i=-4;i<=4;i++)
P1=mynum[i];
}

Write an 8051 C program to toggle bit D0 of the
port P1 (P1.0) 50,000 times.
#include <reg51.h>
sbit MYBIT=P1^0;
void main(void)
{
unsigned int z;
for (z=0;z<=50000;z++)
{
MYBIT=0;
MYBIT=1;
}
}
Note: sbit keyword allows access to the single bits of the SFR
registers

Time delay in C
 There are two ways to create a time delay in
8051 C
 Using the 8051 timer
 Software delay using instructions
 Note that accuracy of the software delay
depends on Compiler choice
 C compiler converts the C statements and
functions to Assembly language
instructions
 Different compilers produce different code

Write an 8051 C program to toggle bits of P1
continuously forever with some delay.
//Toggle P1 forever with some delay in between “on” and “off”
#include <reg51.h>
void main(void)
{
unsigned int x;
for (;;) //repeat forever
{
p1=0x55;
for (x=0;x<40000;x++); //runs loop for 4000 times; without any operation
p1=0xAA;
for (x=0;x<40000;x++); //This will create some delay
}
}

Write an 8051 C program to toggle bits of P1 ports
continuously with a 250 ms delay.
#include <reg51.h>
void MSDelay(unsigned int);
void main(void)
{
while (1) //repeat forever
{
p1=0x55;
MSDelay(250);
p1=0xAA;
MSDelay(250);
}
}
void MSDelay(unsigned int itime)
{
unsigned int i,j;
for (i=0;i<itime;i++)
for (j=0;j<1275;j++);
}

Byte Size I/O
 This slide is intentionally left blank

LEDs are connected to bits P1 and P2. Write an 8051 C
program that shows the count from 0 to FFH (0000 0000 to
1111 1111 in binary) on the LEDs.
#include <reg51.h>
#define LED P2;
void main(void)
{
P1=00; //clear P1
LED=0; //clear P2
while(1)
{
P1++; //increment P1
LED++; //increment P2
}
}
Note: Ports P0 – P3 are byte-accessable and we can use the P0 – P3
labels as defined in the 8051 header file <reg51.h>

Write an 8051 C program to get a byte of data form P1,
wait 1/2 second, and then send it to P2.
#include <reg51.h>
void main(void)
{
unsigned char mybyte;
P1=0xFF; //make P1 input port
while (1)
{
mybyte=P1; //get a byte from P1
MSDelay(500);
P2=mybyte; //send it to P2
}
}
{
unsigned int i,j;
for (j=0;j<1275;j++);
}

Write an 8051 C program to get a byte of data form P0. If it
is less than 100, send it to P1; otherwise, send it to P2.
#include <reg51.h>
void main(void)
{
unsigned char mybyte;
P0=0xFF; //make P0 input port
while (1)
{
mybyte=P0; //get a byte from P0
if (mybyte<100)
else
}
}
{
unsigned int i,j;
for (j=0;j<1275;j++);
}

I/O PROGRAMMING Bit-addressable I/O
 This slide is intentionally left blank

Write an 8051 C program to toggle only bit P2.4
continuously without disturbing the rest of the bits of P2.
//Toggling an individual bit
#include <reg51.h>
sbit mybit=P2^4;
void main(void)
{
while (1)
{
mybit=1; //turn on P2.4
mybit=0; //turn off P2.4
}
}
Note:
 Ports P0 – P3 are bit-addressable and we use sbit data type to
access a single bit of P0 - P3
 Use the Px^y format, where x is the port 0, 1, 2, or 3 and y is the bit
0 – 7 of that port

Write an 8051 C program to monitor bit P1.5. If it
is high, send 55H to P0; otherwise, send AAH to
P2.
#include <reg51.h>
sbit mybit=P1^5;
void main(void)
{
mybit=1; //make mybit an input
while (1)
{
if (mybit==1)
P0=0x55;
else
P2=0xAA;
}
}

A door sensor is connected to the P1.1 pin, and a buzzer is
connected to P1.7. Write an 8051 C program to monitor the door
sensor, and when it opens, sound the buzzer. You can sound the
buzzer by sending a square wave of a few hundred Hz.
#include <reg51.h>
sbit Dsensor=P1^1;
sbit Buzzer=P1^7;
void main(void)
{
Dsensor=1; //make P1.1 an input
while (1)
{
while (Dsensor==1)//while it opens
{
Buzzer=0;
MSDelay(200);
Buzzer=1;
MSDelay(200);
}
}
}
{
unsigned int i,j;
for (j=0;j<1275;j++);
}

Write an 8051 C program to toggle all the bits of
P0, P1, and P2 continuously with a 250 ms delay.
Use the sfr keyword to declare the port addresses.
sfr P0=0x80;
sfr P1=0x90;
sfr P2=0xA0;
void main(void)
{
while (1)
{
P0=0x55;
P1=0x55;
P2=0x55;
MSDelay(250);
P0=0xAA;
P1=0xAA;
P2=0xAA;
MSDelay(250);
}
}
{
unsigned int i,j;
for (j=0;j<1275;j++);
}

The data pins of an LCD are connected to P1. The
information is latched into the LCD whenever its Enable
pin goes from high to low. Write an 8051 C program to
send “ECED-SVNIT” to this LCD.
#include <reg51.h>
#define LCDData P1 //LCDData declaration
sbit En=P2^0; //the enable pin
void main(void)
{
unsigned char message[] =“ECED-SVNIT”;
unsigned char z;
for (z=0;z<10;z++) //send 10 characters
{
LCDData=message[z];
En=1; //a high-
En=0; //-to-low pulse to latch data
}
}

Write an 8051 C program to turn bit P1.5 on and
off 50,000 times.
#include <reg51.h>
sbit MYBIT=0x95;
void main(void)
{
unsigned int z;
for (z=0;z<50000;z++)
{
MYBIT=1;
MYBIT=0;
}
}
Note
 We can access a single bit of any SFR if we specify the bit
address

I/O PROGRAMMING: Using bit
Data Type for Bit-addressable
RAM
 Write an 8051 C program to get the status of bit P1.0, save it, and send
it to P2.7 continuously.
#include <reg51.h>
sbit inbit=P1^0;
sbit outbit=P2^7;
bit membit; //use bit to declare bit- addressable memory
void main(void)
{
while (1)
{
membit=inbit; //get a bit from P1.0
outbit=membit; //send it to P2.7
}
}
 We use bit data type to access data in a bit-addressable section of the data
RAM space 20 – 2FH

Operators in C
 Logical operators
 AND (&&), OR (||), and NOT (!)
 Bit-wise operators
 AND (&), OR (|), EX-OR (^), Inverter (~),
 Shift Right (>>), and Shift Left (<<)

Write an 8051 C program to toggle all the bits of P0 and
P2 continuously with a 250 ms delay. Using the inverting
and Ex-OR operators, respectively.
#include <reg51.h>
void main(void)
{
P0=0x55;
P2=0x55;
while (1)
{
P0=~P0;
P2=P2^0xFF;
MSDelay(250);
}
}

Write an 8051 C program to get bit P1.0 and send it to
P2.7 after inverting it.
#include <reg51.h>
sbit inbit=P1^0;
sbit outbit=P2^7;
bit membit;
void main(void)
{
while (1)
{
membit=inbit; //get a bit from P1.0
outbit=~membit; //invert it and send it to P2.7
}
}

 Write an 8051 C program to read the P1.0 and
P1.1 bits and issue an ASCII character to P0
according to the following table.
P1.1 P1.0
0 0 send ‘0’ to P0
0 1 send ‘1’ to P0
1 0 send ‘2’ to P0
1 1 send ‘3’ to P0

#include <reg51.h>
void main(void)
{
unsignbed char z;
z=P1;
z=z&0x3;
switch (z)
{
Case 0: P0=‘0’;
break;
Case 1: P0=‘1’;
break;
Case 2: P0=‘2’;
break;
Case 3: P0=‘3’;
break;
}
}

DATA CONVERSION: Packed BCD to ASCII
Conversion
Write an 8051 C program to convert packed BCD 0x29 to
ASCII and display the bytes on P1 and P2.
#include <reg51.h>
void main(void)
{
unsigned char x,y,z;
unsigned char mybyte=0x29;
x=mybyte&0x0F;
P1=x|0x30;
y=mybyte&0xF0;
y=y>>4;
P2=y|0x30;
}

DATA CONVERSION: ASCII to Packed BCD
Conversion
Write an 8051 C program to convert ASCII digits of ‘4’ and
‘7’ to packed BCD and display them on P1.
#include <reg51.h>
void main(void)
{
unsigned char bcdbyte;
unsigned char w=‘4’;
unsigned char z=‘7’;
w=w&0x0F;
w=w<<4;
z=z&0x0F;
bcdbyte=w|z;
P1=bcdbyte;
}

DATA CONVERSION: Checksum
Byte
Write an 8051 C program to calculate the checksum byte for the data
25H, 62H, 3FH, and 52H.
#include <reg51.h>
void main(void)
{
unsigned char mydata[ ]={0x25,0x62,0x3F,0x52};
unsigned char sum=0;
unsigned char x;
unsigned char chksumbyte;
for (x=0;x<4;x++)
{
P2=mydata[x];
sum=sum+mydata[x];
}
chksumbyte=~sum+1;
P2=chksumbyte;
}

Write an 8051 C program to perform the checksum
operation to ensure data integrity. If data is good, send
ASCII character ‘G’ to P0. Otherwise send ‘B’ to P0.
#include <reg51.h>
void main(void)
{
unsigned char mydata[
]={0x25,0x62,0x3F,0x52,0xE8};
unsigned char chksum=0;
unsigned char x;
for (x=0;x<5;x++)
chksum=chksum + mydata[x];
if (chksum==0)
P0=‘G’;
else
P0=‘B’;

DATA CONVERSION: Binary (hex) to Decimal and ASCII
Conversion
Write an 8051 C program to convert 11111101 (FD hex) to decimal
and display the digits on P0, P1 and P2.
#include <reg51.h>
void main(void)
{
unsigned char x,binbyte,d1,d2,d3;
binbyte=0xFD;
x=binbyte/10;
d1=binbyte%10;
d2=x%10;
d3=x/10;
P0=d1;
P1=d2;
P2=d3;
}

RAM Data Space Usage by 8051 C Compiler
 The 8051 C compiler allocates RAM locations
 Bank 0 :- addresses 0 – 7
 Individual variables :- addresses 08 and
beyond
 Array elements:- addresses right after
variables
 Array elements need contiguous RAM
locations and that limits the size of the array
due to the fact that we have only 128 bytes of
RAM for everything
 Stack:- addresses right after array elements

ACCESSING CODE ROM
 To make the C compiler use the code space instead of the
RAM space, we need to put the keyword code in front of the
variable declaration
Example:
#include <reg51.h>
void main(void)
{
code unsigned char mynum[ ]=“ABCDEF”;
unsigned char z;
for (z=0;z<=6;z++)
P1=mynum[z];
}

Compare and contrast the following programs and
discuss the advantages and disadvantages of
each one.
#include <reg51.h>
void main(void)
{
unsigned char mydata[]=“HELLO”;
unsigned char z;
for (z=0;z<=5;z++)
P1=mydata[z];
}
(a)
#include <reg51.h>
void main(void)
{
code unsigned char mydata[]=“HELLO”;
unsigned char z;
for (z=0;z<=5;z++)
P1=mydata[z];
}
(b)

 (a) uses the RAM data space to store array
elements, therefore the size of the array is
limited
 (b) uses a separate area of the code space for
data. This allows the size of the array to be as
long as you want if you have the on-chip ROM.
 However, the more code space you use for
data, the less space is left for your program
code

DATA SERIALIZATION
 Serializing data is a way of sending a byte of
data one bit at a time through a single pin of
microcontroller. There are two ways:
 Using the serial port
 Transfer data one bit a time and control the
sequence of data and spaces in between them
(to be studied here)

Write a C program to send out the value 44H
serially one bit at a time via P1.0. The LSB should
go out first.
#include <reg51.h>
sbit P1b0=P1^0;
sbit ACCLSB=ACC^0;
void main(void)
{
unsigned char conbyte=0x44;
unsigned char x;
ACC=conbyte;
for (x=0;x<8;x++)
{
P1b0=ACCLSB;
ACC=ACC>>1;
}
}

Write a C program to send out the value 44H
serially one bit at a time via P1.0. The MSB should
go out first.
#include <reg51.h>
sbit P1b0=P1^0;
sbit ACCMSB=ACC^7;
void main(void)
{
unsigned char sendbyte=0x44;
unsigned char x;
ACC = sendbyte;
for (x=0;x<8;x++)
{
P1b0=ACCMSB;
ACC=ACC<<1;
}
}

Write a C program to bring in a byte of data
serially one bit at a time via P1.0. The LSB should
come in first.
#include <reg51.h>
sbit P1b0=P1^0;
sbit ACCMSB=ACC^7;
bit membit;
void main(void)
{
unsigned char x;
for (x=0;x<8;x++)
{
membit=P1b0;
ACC=ACC>>1;
ACCMSB=membit;
}
P2=ACC;
}

Write a C program to bring in a byte of data
serially one bit at a time via P1.0. The MSB should
come in first.
#include <reg51.h>
sbit P1b0=P1^0;
sbit ACCLSB=ACC^0;
bit membit;
void main(void)
{
unsigned char x;
for (x=0;x<8;x++)
{
membit=P1b0;
ACC=ACC<<1;
ACCLSB=membit;
}
P2=ACC;
}

Intel 8051 Programming in C

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