how to write interrupt service routine in 0004h address

[binu.kr]

I am making a scrolling msg display, usart communication is used to give data directly to display from keyboard and i am shorting rb4 pin with rx pin of usart. If any interrupt comes i want to go to 0x0004 (interrupt vector address) and write a program for usart reception. Please help me to write program in #org 0x0004h location. I am working in pic16f877a and mplab v8.0, pcw compiler ide version 3.36. Can u please help me.
_________________
nn

[Ttelmah]

The interrupt handler, has to do quite a bit of 'housekeeping'.
When the interrupt occurs, the processor calls the code at address '4', and the code here, _must_ save any 'in use' registers, _before_it starts to do it's own work. Then after finishing, these registers need to be restored, before returning to the main code. Also, if there is more than one interrupt, the code needs to work out which one has occurred, and call the correct routine.
Hence the code at address '04', needs to be more than just your routine. The way interrupts are handled in CCS, depends on how you want to deal with the needs for this housekeeping.
The simplest approach, will normally work fine:

[binu.kr]

thank u for ur reply
But i am still in problem while i am using interrupt service routine the
program doesn't go to the main function. It only go to the
void serial_receive (void )
When i press a key in the keyboard, I want to go main function and
execute the main program. If usart interrupt comes it must go to the
service routine and after completing the service routine it must return
to main function. Pls help me to solve this problem.


this is my testing code

[Ttelmah]

First, get rid of the RETFIE....
By adding this, you have bypassed the housekeeping on the return, and everything will go wrong.
Then, get rid of the delay, and the EEPROM write....
The problem is that an EEPROM write takes about 4mSec, and the delay, another 5. Put together, the routine now takes about 9mSec. Serial characters at (say) 9600bps (you don't show your serial setup, so we can't tell what rate you are using), can arrive about every mSec. Hence, after one character, you are still inside the routine, and things _will_ go wrong. You need to get out of the interrupt handler ASAP.
Look at EX_SISR, which shows how to write received characters into a circular buffer. Then in your 'main', check if a character is in the buffer, and if so, write it to the EEPROM.
However, then another caveat. The EEPROM, has a relatively short 'write' life (in the case of the chip you are using, a minimum of 100K cycles). If you wrote a character every 4mSec (the typical write time), you could destroy the EEPROM in under 7 minutes. The EEPROM, is _not_ designed for continuous updates like this.

Best Wishes

[binu.kr]

thanks for your reply.....your reply helped me to solve most of the problem in my program...
_________________
nn

[binu.kr]

how to avoid glare in scrolling message display
PostPosted: Sat Aug 02, 2008 3:30 am Reply with quote Edit/Delete this post Delete this post
iam making a 10 character 5*7 scrolling led display using pic 16f877a....but in night it glows with glare ,can u please give me a solution to overcome this problem,glare is in next line onlymeans coming line, iam using shift register to give positive voltage to led,......pls help me to solve this problem


my display loop is



for(p1=0;p1<50;p1++)
{
V2=temp5[P1];
#ASM

BCF PORTC,3...clk to shift register
NOP
NOP

CALL DELAY1
BSF PORTC,3
MOVF V2,0
MOVWF PORTD
CALL DELAY1
#ENDASM

}

OUTPUT_BIT(PIN_C0,0);
#ASM
CALL DELAY1
#ENDASM


iam using asm inside because while iam using c code for display loop more glare is coming


my c loop,spi ptrotocol used to write value 0x01 to shiftregister

for(p1=0;p1<50;p1++)
{

OUTPUT_BIT( PIN_C3,0); shift register clock
DELAY();
OUTPUT_BIT( PIN_C3,1);
output_d(temp5[p1]);
DELAY();
}

OUTPUT_BIT(PIN_C0,0);
DELAY();
thank u ......
_________________
nn