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keil C Programming Tutorial: Pointers

►Pointers in Keil C

Pointers in keil C is are similar to that of standard C and can perform all the operations that are available in standard C.

In addition, keil C extends the operatability of pointers to match with the 8051 Controller architecture. Keil C provides

two different types of pointers:

Generic Pointers1.

Memory-Specific Pointers2.

►Generic Pointers:

Generic Pointers are declared same as standard C Pointers as shown below:

CODE:

char *ptr; //Character Pointer

int *num; //Integer Pointer

Generic pointers are always stored using three bytes. The first byte is the memory type, the second byte is the

high-order byte of the offset, and the third byte is the low-order byte of the offset. Generic pointers maybe used to

access any variable regardless of its location.

►Memory-Specific Pointers:

Memory specific pointers are defined along with memory type to which the pointer refers to, for example:

CODE:

char data *c;

//Pointer to character stored in Data memory

char xdata *c1;

//Pointer to character stored in External Data Memory.

char code *c2;

//Pointer to character stored in Code memory

As Memory-Specific pointers are defined with a memory type at compile time, so memory type byte as required for

generic pointers is not needed. Memory-Specific pointers can be stored using 1 byte (for idata, data, bdata and pdata

pointers) or 2 bytes (for code and xdata pointers).

The Code generated by keil C compiler for memory-specific pointer executes mroe quickly than the equivalent codegenerated for a generic pointer. This is because the memory area accessed by the pointer is known at the compile timerather at run-time. The compiler can use this information to optimize memory access. So If execution speed is yourpriority then it is recommended to use memory-specific pointers.

Generic pointers and Memory-Specific pointers can be declared with memory area in which they are to be stored. For

example:

CODE:

//Generic Pointer

char * idata ptr;

//character pointer stored in data memory

int * xdata ptr1;

//Integer pointer stored in external data memory

//Memory Specific pointer

char idata * xdata ptr2;

//Pointer to character stored in Internal Data memory

//and pointer is going to be stored in External data memory

int xdata * data ptr3;

//Pointer to character stored in External Data memory

//and pointer is going to be stored in data memory

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Chatbox

sks | 05 Nov : 09:51

Hi Everybody,

Good morning

sks

jeeson | 05 Nov : 07:30

@boots

hi

Coitsu | 04 Nov : 22:05

Hi, i've recently posted a reply in

my "home automation against

earthquakes using pic and sensors"

if some1 can help me

Anonymous | 04 Nov : 21:39

hi ajay! i have tested rc5 remote in

p89v51rd2 and 89s52. working. i

need some modification so that the

output is not latched ie. output is

high, as long as i keep the buttons

pressed

sks | 04 Nov : 18:29

Hi all

Good evening

sks

Anonymous | 04 Nov : 07:45

hi

aniket.hello | 03 Nov : 08:10

hello ajay...plz reply to my forum....

m already late to submit my

project....

eng11 | 03 Nov : 06:01

Thanks Ajay and Majoka for the info

i will wait to see if he reply to your

message

and thanks again guys

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ravi111 | 02 Nov : 20:31

hello sir

i want information about how to

make modern treadmill.

aniket.hello | 02 Nov : 19:19

heya.....plz reply on my forum

in project green bee....

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