Newbie Programme.

lord loh. · Apr 29, 2006

I am new to microcontrollers and have read the stickey FAQ.

I tried to write a programme for 18F452. The programme is supposed to generate a pulse train of 30% dutycycle.

I tried to simulate it in MP Lab IDE.

Code:

org 0000
movlw 0x03			;Set PORT A to Digital
movwf 0x0fc1

bcf 0x0f92,0		;Set bit0 of PORT A as output

loop:

movlw 0x03			;Output a 30% Duty cycle pulse train.
bsf 0x0f80,0
call delay
bcf 0x0f80,0
movlw 0x07
call delay

goto loop

delay:
dcfsnz 0x00fe8	;decrement W
return
bra delay

END

When I tried to observer the RA0 pin in the logic analyser applet, all I got was a straight line.

Please help

akg · Apr 29, 2006

bsf 0x0f80,0

ooh..using the const defines will make the code more readable...

lord loh. · Apr 30, 2006

So I have to define constants mysef? :cry:
I thought the IDE would understand it.... But it did not...

SO I had to write it all as addresses....

Code:

org 0000
movlw 0x03         ;Set PORT A to Digital 
movwf 0x0fc1         ;ADCON1

bcf 0x0f92,0      ;Set bit0 of PORT A as output (TRISA)

loop:

movlw 0x03         ;Output a 30% Duty cycle pulse train.
bsf 0x0f80,0         ;PORT A but LATA is set
call delay
bcf 0x0f80,0
movlw 0x07
call delay

goto loop

delay:
dcfsnz 0x00fe8   ;decrement W
return
bra delay

END

akg · Apr 30, 2006

the 18F452 should have a header in the mpasm ,just include it , the declaration are all there..

it's there in the \microchip\mpasm suite\

file name is p18F452.inc , include it

lord loh. · Apr 30, 2006

Code:

	org 0000
	#include P18F452.inc
	movlw 0x03			;Set PORT A to Digital
	movwf ADCON1

	bcf TRISA,0		;Set bit0 of PORT A as output

loop:

	movlw 0x03			;Output a 30% Duty cycle pulse train.
	bsf LATA,0
	call delay
	bcf LATA,0
	movlw 0x07
	call delay

	goto loop

delay:
	dcfsnz WREG	;decrement W
	return
	bra delay

	END

Okay I tried to do it...And it builds and runs properly...

Except that I do not see any waveform on the Logic Analyzer when I try to observe AN0 or RA0

Please help...

akg · May 1, 2006

i donno anything abt the 18F..still
does the simulation succeded ?
what is ur operating freq.?
u said a straight line .is it high or low..?
have u checked the chances for the read-modify-write problem.?

lord loh. · May 2, 2006

Logic Analizer

Here is a picture of the Logic Analyzer

akg · May 2, 2006

why are you not using bcf PORTA,0 instead of bcf LATA,0 , are they same.?

lord loh. · May 2, 2006

I had used bcf PORT A,0 before changing it to bcf LATA,0

And it made no difference in the simulations... Both the commands changed the LATA register... It looks like the PORT A is the input Register and LATA the output.

akg · May 2, 2006

does the tris bit are set correctly , in 16f series porta and trisa are in different banks . check any other things u may have overlooked.

lord loh. · May 2, 2006

In the register windowo I see the bits being set and the value of LATA changing... Only that the change does not appear at the output pin.

lord loh. · May 5, 2006

http://forum.microchip.com/tm.aspx?m=160913&mpage=1&key=&#161001

Okay I had made a mistake...

I think I had misread the datasheet, I had to put 0x07 into the ADCON1 to make the pins digital and not 0x03.

Thanks everyone for help.

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