89c51 port epansion with 8255 keil c

[Ronydc]

 hi friends,

i wanted to increase the port pins with the help of 8255  for 89c51 mcu(atmel)

does any one have the c codes  that can work with keil  uvision (or c51 compiler).
i simply require a sample program with which if i  push a switch on any port pin of 89c51 and i can lit an LED connected on a single 8255 port pin.

your help can make a great fevour for me.

[leptro]

hello,
i'am not a keil user nor a 8051 user, here's a link to the 8255 datasheet. http://www.datasheetarchive.com/pdf/496740.pdf
i've read it quickly and seems to be ease to interface.
good luck.

[bugmike25]

It is quite simple all u need to do is declare the ports of the 8255:

Usually this is used:

//First 8255 IC
#define porta1 XBYTE [0x8000]
#define portb1 XBYTE [0x8001]
#define portc1 XBYTE [0x8002]
#define cword1 XBYTE [0x8003]

// Second 8255 IC
#define porta2 XBYTE [0x9000]
#define portb2 XBYTE [0x9001]
#define portc2 XBYTE [0x9002]
#define cword2 XBYTE [0x9003]

//Then set the port functions - input, output etc. See datasheet for more info. example:
cword1 = 0x80;
//Add short delay here


porta1 = 0xff;
etc...............

[Ronydc]

 thanks leptro and bugmike25.

bug, its a nice thing that you have suggested but this do not work with keil. --> xbyte[0x .... ]  // even if we use the absacc.h  header file.

i found out that _at_  key word works well with keil.

like -->  char xdata PA _at_ 0x8000;
            char xdata CR _at_ 0x8003;
and we can take xdata char as-->
            char xdata j;

so that we can put,
void initPPI()
{ /
CR = 0x80; /* set all port for output */
}   

main()
{
while(1)
{
j = PA; /* read total port A into j*/
}
}

now my problem is..  how to read (or write onto) ON A SINGLE PIN of the port..?
can some one try for the code to push a switch on port pin P0.1 and lit an LED on 8255 port pin PA .2  ...?

PLEASE HELP.
THANKS

[bugmike25]

It works for sure with Keil. What version are u using? I use uVision3. You must include that header file:

#include <absacc.h>

[Ronydc]

i am using uvision2... any way. but still my problems stands.
what to do  for the access for a single port pin as i have write in the last paragraph.

[bugmike25]

I just found a more recent source code which isnt mine which uses the commands u used.  They only work with the recent versions of Keil (after ARM bought Keil) because i have an older version and that command does not work.

Now if u need to output on port A, pin 2 of the 8255 u must set ur control word to 1000XXXX = 0x80

This means that the 8255 is set to mode 0: basin i/o operation and port A is set as output.
Now when u are dealing with a port is must be treated at a byte.  Therefore if u need to use another pin on Port A for a completely different application you can do this:

Create a variable of unsigned char temp=0,
Then use a variable of type bit to set the state of ur LED; name it LED1,
Then set temp = temp|LED1;
and then shift left using the << command to place the bit in the correct position. This can be done for many different LEDx states.

Then using portA = temp;

However, u cannot just set a single bit on the 8255, you must treat is as a byte.

[Ronydc]

THX BUG ,
in short i got it, that as you said, the same can be done in following way.
if i want to lit a single led on any port pin.. i have to put there a port value.
like PA = 0X10;  or PA = 20; ( this is ment for some pins on and some off..)
and like tht the port value for the  required port pin.
yes.. this enlitans my mind... dear friend..!!

THANKS.

thanks a lot for your quick helps.

[sjn]

#define LCD_DATA     XBYTE [0xE000] // Port A
#define KEY_OUT      XBYTE [0xE001] // Port B
#define KEY_IN        XBYTE [0xE002] // Port C
#define CONTROL_PORT     XBYTE [0xE003] // Control Port

#define CONTROL_WORD   0x89  // Port A => O/P , B => O/P , C => I/P



.....

void main(void)
{
   unsigned char j;
   delay(1000);

   CONTROL_PORT = CONTROL_WORD;
             ...
             LCD_DATA  = 0x00;
}

[Ronydc]

we had a good discussion abt 8255 ports and pins . thanks friends.

but i have found the shortest way for solving my fundamental problem. and that is--> to use the switches in matrix form. i can use as many switches i like if thay are in matrix.
and the output too i suppose.
thanks any way.