Programming timer0 in PIC 16f628

mshemyalnisar · Nov 22, 2008

I need some help in a project of mine, for the part regarding timer0 and I am using PIC 16f628.

the statement of the question goes:

"Write a peripheral program to generate PRECISE 1 ms delay."

I need this help urgently..... somebody plzzzzzzzzzzzzz.......

blueroomelectronics · Nov 22, 2008

Sounds like a homework assignment.

mshemyalnisar · Nov 22, 2008

yes it is........... a small part of it.............

and I need help.............

BeeBop · Nov 22, 2008

mshemyalnisar said:
I need some help in a project of mine, for the part regarding timer0 and I am using PIC 16f628.

the statement of the question goes:

"Write a peripheral program to generate PRECISE 1 ms delay."

I need this help urgently..... somebody plzzzzzzzzzzzzz.......

Read this and you should be able to do it:

mshemyalnisar · Nov 23, 2008

this link is not pic 18f

can anyone give me the timer0 code for a pic 16f628 plzzzzzzz which would generate 1 ms delay......

Diver300 · Nov 23, 2008

MPLAB is free. It has a stopwatch in the simulator, so you can easily test delays. PICLIST has lots of examples of delay.

You'll learn a lot by doing it yourself.

mshemyalnisar · Nov 23, 2008

I just want to get done with this project of the course i never even wanted to do..........

so plzzzzzzzzz is there anyone who can help me here???

Pommie · Nov 23, 2008

I'll give you a starter, if you have a 4MHz crystal then your pic will run at 1MHz. Set the prescaler to 4 and preload timer0 with 6 (256-6 = 250, 250*4=1000). Timer0 interrupt flag (T0IF) will become set after 1mS.

HTH.

Mike.

mshemyalnisar · Nov 23, 2008

I have set my options register as:

bcf OPTION_REG, 5 ;
bcf OPTION_REG, 3 ;
bsf OPTION_REG, 0 ;

is this ok??

Pommie · Nov 23, 2008

You have assumed that the option register starts out as zero. It defaults to 0xff.

Mike.

mshemyalnisar · Nov 23, 2008

so should i set it as :

"11000001"

to make the prescaler equal to 4??

HELPPPPPPPPPPPPppppppppp............

Pommie · Nov 23, 2008

Yes, that would set the prescaler to 4.

Next, write 250 (0xfa) to TMR0, clear bit T0IF, and 1mS later T0IF will be set again.

Mike.

mshemyalnisar · Nov 23, 2008

ok i think i have done it............

i have tried to write the following code where the next LED would flash every 1 ms. meaning the rotate function is used......

bsf STATUS,5 ;
movlw 00H ;
movwf TRISB ;
movlw B'1111' ;
movwf TRISA ;
bcf STATUS,5 ;
movlw 00H ;
movwf PORTB ;
bcf OPTION_REG, 5 ;
bcf OPTION_REG, 3 ;
bsf OPTION_REG, 0 ;
bsf intcon, 1 ;

func
bcf, intcon , 2 ;
rrf PORTB , 1 ;
movlw 0xfa ;
movwf TMR0 ;
goto check ;
return;

main
movlw 01H ;
movwf PORTB ;
movlw 0xfa ;
movwf TMR0 ;
check btfss intcon, 2 ;
goto func ;
goto check ;
end;

mshemyalnisar · Nov 24, 2008

somebody please helpppppppppppppppppppp

ericgibbs · Nov 24, 2008

mshemyalnisar said:
somebody please helpppppppppppppppppppp

Please post your full program.

BTW: I would suggest you dont use 'helpppppppppppppppppppp' it just 'P's' people off.

gramo · Nov 24, 2008

If you were using a higher language, it would be pretty simple

Written for a 16F628A with a 4Mhz crystal. It creates a loop that delays for 1mS and then repeats.

Written with **broken link removed**

Code:

Device = 16F628A
Xtal = 4
   		   
Dim uS as Word
Dim mS as Word

Symbol GIE = INTCON.7				' Global Interrupt Enable Bit
Symbol TMR0_uS = 512		  		' Set time interval of TMR0
Symbol TMR0_Enable = INTCON.5			' This option enables TMR0 interrupts
Symbol TMR0_Overflow = INTCON.2			' This is the TMR0 overflow flag
			
ON_INTERRUPT Int_Sub

Goto Initialization			
			
Int_Sub:

	GIE = 0
	If TMR0_Overflow = 1 And TMR0_Enable = 1 Then
	   TMR0_Overflow = 0
	   uS = uS + TMR0_uS
	   If uS >= 1000 Then
	   	  uS = uS - 1000
	  	  mS = mS + 1
	   EndIf
	EndIf
	
	GIE = 1
	
	Context Restore
	
Initialization:
	
	TMR0_Enable = 0	   	   	 	' Disable TMR0 interrupts
	
	uS = 0		  			' Clear timer registers
	mS = 0		  			' 

	OPTION_REG.0 = 0   			'000	-	1 : 2
	OPTION_REG.1 = 0   			'
	OPTION_REG.2 = 0			
	OPTION_REG.5 = 0			' Select Internal Clock Source

	TMR0 = 0	   			' Clear the TMR0 register
	
	TMR0_Enable = 1				' Enable TMR0 Interrupts
	
	GIE = 1		  			' Enable Global Interrupts
		
Main:

	Repeat 					' Create a loop
	
	Until mS = 1 				' Wait for 1 mS

	mS = 0		 	 		' Clear the mS register
	
	Goto Main				' Loop for ever

mshemyalnisar · Nov 24, 2008

the task that i am trying to implement is use a timer0 to generate a delay of 1ms and after every 1 ms the next led on portB would light up and and previous one would turn off. this task is to be done without using ISR......

the program that i made is:

org 0x00
;goto main;

PORTB EQU 0x06;
PORTA EQU 0x05;
TRISA EQU 0x85;
TRISB EQU 0x86;
STATUS EQU 0X03;
INPUT EQU 0X07;

bsf STATUS,5 ;
movlw 00H ;
movwf TRISB ;
movlw B'1111' ;
movwf TRISA ;
bcf STATUS,5 ;
movlw 00H ;
movwf PORTB ;
movlw b'11000001' ;
movwf option_reg ;
bsf intcon, 7 ;

func
bcf, intcon , 2 ;
rrf PORTB , 1 ;
movlw 0xfa ;
movwf TMR0 ;
goto check ;
return;

main
movlw 01H ;
movwf PORTB ;
movlw 0xfa ;
movwf TMR0 ;
check btfss intcon, 2 ;
goto func ;
goto check ;
end;

mshemyalnisar · Nov 24, 2008

I can not use a higher language as i have to do it in assembly as per the requirements of the project

Pommie · Nov 24, 2008

Your code is close to working. See below,

Code:

		org	0x00 
;goto main;

PORTB		equ	0x06		;
PORTA		equ	0x05		;
TRISA		equ	0x85		;
TRISB		equ	0x86		;
STATUS		equ	0X03		;
INPUT		equ	0X07		;

		bsf	STATUS,5
		movlw	00H	
		movwf	TRISB	
		movlw	B'1111'	
		movwf	TRISA	
		bcf	STATUS,5
		movlw	00H	
		movwf	PORTB	
		movlw	b'11000001'
		movwf	option_reg
	;;	bsf	intcon,7  <<<------remove this

func
		bcf	intcon,2
		bcf	STATUS,C	;required so only 1 bit set
		rrf	PORTB,1	
		movfw	PORTB		;this is required
		btfsc	STATUS,Z	;otherwise port B
		bsf	PORTB,7		;will end up zero
		movlw	0xfa	
		movwf	TMR0	
		goto	check	
return;


main
		movlw	01H	;\
		movwf	PORTB	; | This is never
		movlw	0xfa	; | executed
		movwf	TMR0	;/
check		btfs[COLOR="Red"]c[/COLOR]	intcon,2   ;<-- changed
		goto	func
		goto	check
end;

You had your test the wrong way around.

You also need config data for it to work in a chip.

Mike.

gramo · Nov 24, 2008

mshemyalnisar said:
I can not use a higher language as i have to do it in assembly as per the requirements of the project

No worries, I was just putting it out there. Plenty of resident assembly gurus to help you out here at electro tech

Programming timer0 in PIC 16f628

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