Introduction

The use of C language to program microcontrollers is becoming too common. And most of the time its not easy to buld an application in assembly which instead you can make easily in C. So Its important that you know C language for microcontroller which is commonly known as Embedded C. As we are going to use Keil C51 Compiler, hence we also call it Keil C.

Keywords

Keil C51 compiler adds few more keywords to the scope C Language:

_at_ far sbit
alien idata sfr
bdata interrupt sfr16
bit large small
code pdata _task_
compact _priority_ using
data reentrant xdata
data/idata

Description: The variable will be stored in internal data memory of controller. example:

unsigned char data x;
//or
unsigned char idata y;
		
bdata

Description: The variable will be stored in bit addressable memory of controller. example:

unsigned char bdata x;
//each bit of the variable x can be accessed as follows
x ^ 1 = 1; //1st bit of variable x is set
x ^ 0 = 0; //0th bit of variable x is cleared
		
xdata

Description: The variable will be stored in external RAM memory of controller. example:

unsigned char xdata x;
		
code

Description: This keyword is used to store a constant variable in code memory. Lets say you have a big string which is not going to change anywhere in program. Wasting ram for such string will be foolish thing. So instead we will make use of the keyword "code" as shown in example below. example:

unsigned char code str="this is a constant string";
		
pdata

Description: This keyword will store the variable in paged data memory. This keyword is used occasionally. example:

unsigned char pdata x;
		
_at_

Description: This keyword is used to store a variable on a defined location in ram. example:

unsigned char idata x _at_ 0x30;
// variable x will be stored at location 0x30
// in internal data memory
		
sbit

Description: This keyword is used to define a special bit from SFR (special function register) memory. example:

sbit Port0_0 = 0x80;
// Special bit with name Port0_0 is defined at address 0x80
		
sfr

Description: sfr is used to define an 8-bit special function register from sfr memory. example:

sfr Port1 = 0x90;
// Special function register with name Port1 defined at addrress 0x90
		
sfr16

Description: This keyword is used to define a two sequential 8-bit registers in SFR memory. example:

sfr16 DPTR = 0x82;
// 16-bit special function register starting at 0x82
// DPL at 0x82, DPH at 0x83
		
using

Description: This keyword is used to define register bank for a function. User can specify register bank 0 to 3. example:

void function () using 2
{
	// code
}
// Funtion named "function" uses register bank 2 while executing its code
		
interrupt

Description: This keyword will tells the compiler that function described is an interrupt service routine. C51 compiler supports interrupt functions for 32 interrupts (0-31). Use the interrupt vector address in the following table to determine the interrupt number.

Interrupt vector
example:

void External_Int0() interrupt 0
{
	//code
}
		

Memory Models

There are three kind of memory models available for the user:

Small
All variables in internal data memory.
Compact
Variables in one page, maximum 256 variables (limited due to addressing scheme, memory accessed indirectly using r0 and r1 registers)
large
All variables in external ram. variables are accessed using DPTR.
Depending on our hardware configuration we can specify the momory models as shown below:

//For Small Memory model
#pragma small
//For Compact memory model
#pragma compact
//For large memory model
#pragma large
		

Conversation

ExperimenterUK
Sat Sep 13 2014, 12:34 PM
jaimin1212,Pimpalkhare Create a thread for your question
jaimin1212
Sat Sep 13 2014, 02:35 AM
i want to make self balancing robot using MPU6050 using atmega8.. please help to get data of gyro and accelerometer from this sensor through atmega8.
Thu Sep 11 2014, 09:00 AM
Sunil Pimpalkhare
Hello sir, I am trying to make Wearfin project https://www.youtube.com/watch?v=iZ6PVBvQf-g so can u help me in teaching how to built the program???
Thu Sep 11 2014, 02:21 AM
hariom panday
plz hlp me in my project
iec.naga
Tue Sep 09 2014, 01:19 AM
spi
Mon Sep 08 2014, 08:14 AM
fameem
water changing in fish tank automatically using microcontoller with timer. send idea to me
dexter_a
Sat Sep 06 2014, 11:09 AM
hello guys
Sat Sep 06 2014, 10:10 AM
munaxa
plx guide me
Sat Sep 06 2014, 10:09 AM
munaxa
hi i want to buy plx guie me
ajay_bhargav
Sat Sep 06 2014, 03:10 AM
@Ben, Its hard to undrstand the context like this. If you can post in forum with some example code we might answer you better.

Downloads

Comments

deepbhadani
Fri Sep 19 2014, 01:08 PM
desaiakshay92
Fri Sep 19 2014, 12:45 AM
Fiddu
Thu Sep 18 2014, 02:28 AM
piku_123
Tue Sep 16 2014, 11:29 AM
qudor
Tue Sep 16 2014, 11:06 AM
sara_seecs
Tue Sep 16 2014, 10:53 AM
akshar
Fri Sep 12 2014, 12:45 PM
iec.naga
Tue Sep 09 2014, 01:09 AM

Online

Guests: 72, Members: 0 ...

most ever online: 182184
(Members: , Guests: 182184) on 06 Aug 2010: 01:37 AM

Members: 37517
Newest member: deepbhadani
Forum Activity
kirangowle Avatar
Posted By kirangowle
Sat Sep 20 2014, 12:35 AM
Hello All,I want to connect normal speaker (as a s...
ajay_bhargav Avatar
Posted By ajay_bhargav
Wed Sep 17 2014, 12:59 AM
I think its important to list out the features of ...
ajay_bhargav Avatar
Posted By ajay_bhargav
Wed Sep 17 2014, 12:45 AM
you need to put a wait condition in ISR till the s...
akshar Avatar
Posted By akshar
Mon Sep 15 2014, 04:41 AM
sir,i used microcontroller 89v51rd2 in circuit. No...
bobparihar Avatar
Posted By bobparihar
Mon Sep 15 2014, 02:24 AM
i am programming interrupt 0 using 8051my task is....
ExperimenterUK Avatar
Posted By ExperimenterUK
Sat Sep 13 2014, 12:23 PM
There may not be an exact equivalent .You will hav...
akshar Avatar
Posted By akshar
Sat Sep 13 2014, 03:18 AM
Sir, Good Morning,Thank you for making me a member...
ajay_bhargav Avatar
Posted By ajay_bhargav
Thu Sep 11 2014, 12:52 AM
which compiler are you using? I suggest XC8 with M...
ajay_bhargav Avatar
Posted By ajay_bhargav
Thu Sep 11 2014, 12:49 AM
I always prefer Olimex Dev boards when it comes to...
ajay_bhargav Avatar
Posted By ajay_bhargav
Thu Sep 11 2014, 12:44 AM
master will always lower down the Chip select... s...