Chapter 7 8051 programming in c

1
Chapter 7
8051 Programming in C

2
Sections
7.1 Data types and time delay in 8051 C
7.2 I/O programming in 8051 C
7.3 Logic operations in 8051 C
7.4 Data conversion programs in 8051 C
7.5 Accessing code ROM space in 8051 C
7.6 Data serialization using 8051 C

3
Why Program the 8051 in C
• It is easier and less time consuming to write 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 microcontrollers with
little or no modification.

1. if statement (selection) Structure
5

6
2. switch statement (selection) Structure

3. while Looping (Repetition) Structure
7

4. for Looping (Repetition) Structure
8

9
Translation between C and Assembly
• A loop in Assembly
MOV R2,#255
ABC:MOV P1,R2
DJNZ R2,ABC
• A for-loop in C
for (int z=255; z>0; z--)
P1=z;

10
Section 7.1
Data Types and Time Delay in 8051 C

11
Re-examine C Data Type
• Understanding the data types of C can help
programmers to write an efficient code.
• We will focus on (See Table7-1)
– unsigned char, signed char
– unsigned int, signed int,
– Single bit: sbit (sfr) , bit (bit-addressable RAM)
– Special function register: sfr
• C compiler will allocate a RAM space for your
variables (char, int & bit).

12
Table 7-1. Some Widely Used Data Types
for 8051 C

13
Unsigned Char
• The most widely used data types for the 8051
• 8-bit data type
• The range of unsigned char: 0-255 (00-FFH)
• When do you use unsigned char?
– To set counter value (Example 7-1)
– The string of ASCII character (Example 7-2)
– For toggling ports (Example 7-3)

14
Signed Char
• 8-bit data type
• 2’s complement representation
• The range of unsigned char: -128:+127 (00-FFH)
• When do you use signed char?
– To present a given quantity such as temperature

15
Example 7-1 (unsigned char)
Write an 8051 C program to send values 00-FF to port P1.
Solution:
#include <reg51.h>
void main(void)
{
unsigned char z;
for (z=0; z<=255; z++)
P1=z;
}

16
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.
Solution:
#include <reg51.h>
void main(void){
unsigned char mynum[]=“012345ABCD”;
unsigned char z;
for (z=0; z<10; z++)
P1=mynum[z];
}
Note: “012345ABCD” is stored in RAM and can be changed.

17
Write an 8051 C program to toggle all the bits of P1
continuously.
Solution:
#include <reg51.h>
void main(void) {
for ( ; ; ) { //repeat forever
P1=0x55; //0x: in hex (binary)
P1=0xAA;
}
}

18
Example 7-4 (signed char)
Write an 8051 C program to send values of -4 to 4 to port P1.
Solution:
#include <reg51.h>
void main(void)
{
char mynum[]={+1,-1,+2,-2,+3,-3,+4,-4};
unsigned char z;
for (z=0; z<8; z++)
P1=mynum[z];
}

19
Integer
• 16-bit data type
– The range of unsigned int: 0-65535
– The range of signed int: -32,768-32,767
• Since the 8051 is an 8-bit microcontroller and the
int data type takes two bytes of RAM, we must not
used the int data type unless we have to.
• You should try to use unsigned char instead on int.

20
Example 7-5 (unsigned int, sbit)
Write an 8051 C program to toggle bit D0 of P1 50,000 times.
Solution:
#include <reg51.h>
sbit MYBIT=P1^0;
void main(void) {
unsigned int z;
for (z=0;z<50000;z++) {
MYBIT=0;
MYBIT=1;
}
}

21
Time Delay
• Three factors that can affect the accuracy of the
time delay:
– Crystal frequency of 8051 system
– 8051 machine cycle timing
– Compiler used for 8051 C

22
Example 7-6 (time delay)
Write an 8051 C program to toggle bits of P1 continuously
forever with some delay.
Solution:
#include <reg51.h>
void main(void) {
unsigned int x;
for (;;) {
P1=0x55;
for (x=0;x<40000;x++); //time delay
P1=0xAA;
for (x=0;x<40000;x++); }}

23
Example 7-7 (1/2)
Write an 8051 C program to toggle bits of P1 continuously with a
250 ms delay. Solution:
#include <reg51.h>
void MSDelay(unsigned int);
void main(void) {
while(1) { //repeat forever
P1=0x55;
MSDelay(250); //time delay
P1=0xAA;
MSDelay(250) }} Assume the program is tested
for the DS89C420 with XTML=11.0592MHz.
90ns X 1275 = 114750ns = 1ms
void MSDelay(unsigned int itime) {
unsigned int i,j;
for (i=0; i<itime; i++)
for (j=0; j<1275; j++); // 1ms delay}

24
Section 7.2
I/O programming in 8051 C
• Way to access SFR and single bit of SFR
• Access Bit-addressable RAM

25
Access SFR
• Way to access SFR
Use name of SFR and reg51.h
#include <reg51.h>
P1=0x55; //P1=55H
• reg51. h is necessary.
• See Example 7-1.
2. Use the sfr data type and declare by yourself
sfr P1 = 0x90;
P1=0x55; //P1=55H
• reg51. h is not necessary.

28
Access SFR
• Way to access SFR
1. Use name of SFR and reg51.h
#include <reg51.h>
P1=0x55; //P1=55H
• reg51. h is necessary.
2. Use the sfr data type and
declare by yourself
sfr P1 = 0x90;
P1=0x55; //P1=55H

29
Example 7-16 Use the sfr data type andeclare by yourself
Write an 8051 C program to toggle all the bit of P0, P1
and P2 continuously with a 250 ms time dealy.
Solution (a):
sfr P0 = 0x80; // declare by yourself
sfr P2 = 0xA0; // declare by yourself
// MSDelay is as same as one in
// Example7-1. Ignored it here.
void main(void) {
unsigned int z;
P0=0x55;
P1=0x55;
P2=0x55;
P0=0xAA;
P1=0xAA;
P2=0xAA;
} }

30
Example 7-16 Use name of SFR and reg51.h
Solution (a):
void main(void) {
unsigned int z;
P0=0x55;
P1=0x55;
P2=0x55;
P0=0xAA;
P1=0xAA;
P2=0xAA;
} }

31
Example 7-16 Use name of SFR and reg51.h
Solution (a):
void main(void) {
unsigned int z;
P0=0x55;
P1=0x55;
P2=0x55;
P0=0xAA;
P1=0xAA;
P2=0xAA;
} }
#include <reg51.h>

32
#include <reg51.h>?

34
Access Single Bit of SFR
• Way to access a single bit of SFR
– Use sbit and name of SFR
#include <reg51.h>
sbit MYBIT = P1^5; //D5 of P1
– Use sbit to declare the bit of SFR
and declare by yourself
sbit MYBIT = 0x95; //D5 of P1

35
Example 7-17 (sbit)
Write an 8051 C program to turn bit P1.5 on and off 50,000 times.
Solution (a):
void main(void) {
unsigned int z;
for (z=0;z<50000;z++) {
MYBIT=1;
MYBIT=0;
} }
This program is similar to Example 7-5.
sbit MYBIT = 0x95; // P1^5

36
Example 7-17 (sbit)
Write an 8051 C program to turn bit P1.5 on and off 50,000 times.
Solution (a):
void main(void) {
unsigned int z;
for (z=0;z<50000;z++) {
MYBIT=1;
MYBIT=0;
} }
This program is similar to Example 7-5.
#include <reg51.h>
sbit MYBIT=P1^0;
sbit MYBIT = 0x95; // P1^5

37
Access Bit-addressable RAM
• You can use bit to access one bit of bit-
addressable section of the data RAM space
20H-2FH.
#include <reg51.h>
sbit inbit = P1^0;
bit membit; //C compiler assign a RAM space for mybit
membit = inbit; //Read P1^0 to RAM

38
Example 7-18 (bit)
Write an 8051 C program to get the status of bit P1.0,
save it, and send it to P2.7 continuously.
Solution:
#include <reg51.h>
sbit inbit = P1^0;
sbit outbit = P2^7;
bit membit;
void main(void) {
membit = inbit;
outbit = membit }}

39
Section 7.3
Logic operations in 8051 C

40
Bit-wise Operations in C
• AND &
0x35 & 0x0F = 0x05
• OR |
0x04 | 0x68 = 0x6C
• Exclusive-OR ^
0x54 ^ 0x78 = 0x2C
• Inverter ~
~0x55 = 0xAA
0011 0101
AND 0000 1111
0000 0101
0000 0100
OR 0110 1000
0110 1100
0101 0100
XOR 0111 1000
0010 1100NOT 0101 0101
0000 0101

41
Bit-wise Shift Operation in C
• Shift Right >>
0x9A >> 3 = 0x13
shift right 3 times
0x77 >> 4 = 0x07
shift right 4 times
• Shift Left <<
0x96 << 4 = 0x60
shift left 4 times
1001 1010  0001
0011
0111 0111  0000
0111
1001 0110  0110
0000

42
Table 7-3. Bit-wise Logic Operations for C

43
Example 7-19
Run the following program on your simulator and examine the
results.
Solution:
#include <reg51.h>
void main(void) {
P0=0x35 & 0x0F;
P0=0x04 | 0x68;
P0=0x54 ^ 0x78;
P0=~0x35;
P0=0x9A >> 3;
P0=0x77 >> 4;
P0=0x96 << 4; }

44
Section 7.4
Data conversion programs in 8051 C

45
Data Conversion
• Packed BCD to ASCII conversion
– See Example 7-24
• ASCII to packed BCD conversion
– See Example 7-25
• Checksum byte in ROM
– See Example 7-26, 27, 28 (using +)
• Binary to decimal and ASCII conversion in C
– See Example 7-29( using /, %)

46
Table 7-4. ASCII Code for Digits 0-9

Packed BCD to ASCII conversion
Example 7-24
Write an 8051 C program to convert packed BCD 0x29 to
ASCII and display the bytes on P1 and P2.
Solution:
#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;}
47

ASCII to packed BCD conversion
See Example 7-25
Write an 8051 C program to convert ASCII digits of ‘4’ and ‘7’ to
packed BCD and display them on P1.
Solution:
#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;} 48

Binary to decimal and ASCII conversion in C
See Example 7-29( using /, %)
Write an 8051 C program to convert 11111101 (FD hex) to
decimaland display the digits on P0, P1 and P2. Solution:
#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;} 49

50
Section 7.5
Accessing code ROM space in 8051 C

51
To Store Data
• We have three spaces to store data:
1. the 128 bytes RAM space with address range 00-7FH
• If you declare variables (ex: char) to store data, C compiler
will allocate a RAM space for these variable.
2. Use code space
• External code memory (64K) + on-chip ROM (64K)
• Data is embedded to code or is separated as a data section
3. External data memory for data
• RAM or ROM
• see Chapter 14

52
Data Stored in RAM
• Where are the variables assigned by C compiler?
• 8051 C compiler allocates RAM locations for
variables in the following order:
– Bank 0: addresses 0-7
– Individual variables: addresses 08H and beyond
– Array elements: addresses right after variables
• Array size is limited in 128 bytes RAM.
– Stack: address right after array elements
• Check your simulation tool

53
8052 RAM Space
• 8052 has 256 bytes RAM.
• Based on 8052 architecture, you should
– Use the reg52.h header file.
– Choose the 8052 option when compiling the program.

54
Using ROM to Store Data
• To make C compiler use the code space (on-chip
ROM) instead of RAM space, we can put the
keyword “code” in front of the variable
declaration.
unsigned char mydata[] = “HELLO”
• HELLO is saved in RAM.
code unsigned char mydata[] = “HELLO”
• HELLO is saved in ROM.
• See Example 7-33

55
Example 7-33 (1/3)
Compare and contrast the following programs and discuss the
advantages and disadvantages of each one.
Solution (a):
#include <reg51.h>
void main(void) {
P1=“H”; P1=“E”;
P1=“L”; P1=“L”; P1=“O”;
}
Data is embedded into code.
Simple, short, not flexible.

56
Example 7-33 (2/3)
Solution (b):
#include <reg51.h>
void main(void) {
unsigned char mydata[]=“HELLO”;
unsigned char z;
for (z=0; z<5; z++)
P1 = mydata[z];
}
Data is stored in RAM and does not occupied ROM.

57
Example 7-33 (3/3)
Solution (c):
#include <reg51.h>
void main(void) {
code unsigned char mydata[]=“HELLO”;
unsigned char z;
for (z=0; z<5; z++)
P1 = mydata[z];
}
Data is stored in ROM. However, data and code are separate.

58
Section 7.6
Data serialization using 8051 C

59
Serializing Data
• Two ways to transfer a byte of data:
1. Using the serial port.
• For PC. See Chapter 10.
2. To transfer data one bit a time and control the sequence
of data and spaces in between them.
• For LCD, ADC, ROM
• Example 7-34

60
Example 7-34
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.
Solution:
#include <reg51.h>
sbit P1b0 = P1^0;
sbit regALSB = ACC^0;
void main(void) {
unsigned char conbyte = 0x44;
unsigned char x;
ACC = conbyte;
for (x=0; x<8; x++) {
P1b0 = regALSB;
ACC = ACC >> 1; }
}
ACC P1.0
D7 D0

Chapter 7 8051 programming in c

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