Building a stopwatch with PIC16F877a - Electronic Circuits Projects Diagrams Free

ag501 · 22nd November 2007, 11:29 PM

hi all

im having problem with writing assembly language that will implement a stopwatch!!!

i have to design it so that it has a count to the base 7 and has max count of 66!
i also have to implement a delay of 1.38s for each count(i.e time taken for it to go from 1 value to the next) the clock is 20MHz and each instruction takes 200ns!

any help will be appreciated

blueroomelectronics · 23rd November 2007, 01:39 AM

Why do you "have" to design it that way?

Posting your code would help.

Pommie · 23rd November 2007, 03:17 AM

Here's a code snippet that may help. It sets up timer 1 so that it overflows every 10mS.

Code:

		movlw	B'00000001'
		movwf	T1CON;		enable timer 1

		movlw	low(.50000)
		movwf	CCPR1L
		movlw	high(.50000)
		movwf	CCPR1H
		movlw	B'00001011';	enable special event trigger on CCP1
		movwf	CCP1CON;

The bit that gets set is PIR1,CCP1IF and you need to clear it afterwards. So your main code would be something like,

Code:

Wait		btfss	PIR1,CCP1IF
		goto	Wait
		bcf	PIR1,CCP1IF;	reset special event trigger bit
		incf	........etc

HTH

Mike.

Mike.

ag501 · 23rd November 2007, 11:14 AM

hey

i have to design it that way because its part of the specification for my project!!!

that snippet you sent is that for the pic16f877a(20MHz clock,200ns intruction cycle)

**Nigel Goodwin** · 23rd November 2007, 11:22 AM

Quote:

Originally Posted by blueroomelectronics

Why do you "have" to design it that way?

Because it's obviously a school assignment! - the stupid base 7 requirement is probably to stop them just copying something off the net?.

ag501 · 23rd November 2007, 12:55 PM

alrite

i think i have got the counter to count to the base7 but its the delay of 1.38s
im having problem with

**Nigel Goodwin** · 23rd November 2007, 02:58 PM

Quote:

Originally Posted by ag501

alrite

i think i have got the counter to count to the base7 but its the delay of 1.38s
im having problem with

Try the "delay code generator" on the PICList.

Pommie · 23rd November 2007, 03:12 PM

Just use the code I posted earlier. Test the bit and increment a counter, once it gets to 138 your 1.38s is up.

Mike.

Mike, K8LH · 23rd November 2007, 03:21 PM

Mike (Pommie) actually provided a workable 10 msec timer solution. The OP really just needs to add a counter that counts 138 of those timer 'ticks' before incrementing his digit counters. Gosh, how hard could it be?

Code:

;
;
Wait    btfss   PIR1,CCP1IF     ; 10 msec timeout?
        goto    Wait            ; no, branch and wait, else
        bcf     PIR1,CCP1IF     ; clear Timer 1 interrupt flag
        decfsz  Timer,F         ; has 1380 usecs elapsed?
        goto    Wait            ; no, branch, else
        movlw   d'138'          ; reset 1380 usec Timer var'
        movwf   Timer           ; 
;
;  increment digit counters here then jump back to the Wait sub'
;

Pommie · 23rd November 2007, 04:03 PM

Mike,

Your absolutely spot on except for the bit that is set. It is PIR1,CCP1IF that gets set rather than the timer1 interrupt flg.

Mike.

Mike, K8LH · 23rd November 2007, 06:02 PM

Oops! Please pardon me. I corrected my previous post.

ag501 · 25th November 2007, 09:47 PM

hey all
what is PIR1,CCP1IF? are these variables set at the start of the prog?

is the very early ppost u put up is that the beginning of the 10msec delay?

thanks again

Quote:

Originally Posted by Mike, K8LH

Mike (Pommie) actually provided a workable 10 msec timer solution. The OP really just needs to add a counter that counts 138 of those timer 'ticks' before incrementing his digit counters. Gosh, how hard could it be?

Code:

;
;
Wait    btfss   PIR1,CCP1IF     ; 10 msec timeout?
        goto    Wait            ; no, branch and wait, else
        bcf     PIR1,CCP1IF     ; clear Timer 1 interrupt flag
        decfsz  Timer,F         ; has 1380 usecs elapsed?
        goto    Wait            ; no, branch, else
        movlw   d'138'          ; reset 1380 usec Timer var'
        movwf   Timer           ; 
;
;  increment digit counters here then jump back to the Wait sub'
;

ag501 · 26th November 2007, 11:48 AM

hi
i was on the PICList website and looking at the delay code generator
... it uses an instruction similar to this goto $+1?
what does the $ sign mean?

**Nigel Goodwin** · 26th November 2007, 11:59 AM

Quote:

Originally Posted by ag501

hi
i was on the PICList website and looking at the delay code generator
... it uses an instruction similar to this goto $+1?
what does the $ sign mean?

It's explained in the MPASM helpfile, and has been explained here numerous times - $ is the current address - so 'goto $+1' jumps to the following line, essentially a two instruction time NOP.

Pommie · 26th November 2007, 02:48 PM

Quote:

Originally Posted by ag501

hey all
what is PIR1,CCP1IF? are these variables set at the start of the prog?

is the very early ppost u put up is that the beginning of the 10msec delay?

thanks again

PIR1,CCP1IF is a bit that gets set very 10mS if you insert the code snippet that I posted earlier in your initialisation code.

Mike, K8LH posted example code to show how you would use this bit.

It sounds like you need to familiarise yourself with the pic opcodes. Having a read of the sticky and working your way through some of the tutorials would be a good way to learn.

Mike.

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22nd November 2007, 11:29 PM	#1
ag501	Building a stopwatch with PIC16F877a hi all im having problem with writing assembly language that will implement a stopwatch!!! i have to design it so that it has a count to the base 7 and has max count of 66! i also have to implement a delay of 1.38s for each count(i.e time taken for it to go from 1 value to the next) the clock is 20MHz and each instruction takes 200ns! any help will be appreciated

23rd November 2007, 01:39 AM	#2
blueroomelectronics	Why do you "have" to design it that way? Posting your code would help. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com/

23rd November 2007, 03:17 AM	#3
Pommie	Here's a code snippet that may help. It sets up timer 1 so that it overflows every 10mS. Code: movlw B'00000001' movwf T1CON; enable timer 1 movlw low(.50000) movwf CCPR1L movlw high(.50000) movwf CCPR1H movlw B'00001011'; enable special event trigger on CCP1 movwf CCP1CON; The bit that gets set is PIR1,CCP1IF and you need to clear it afterwards. So your main code would be something like, Code: Wait btfss PIR1,CCP1IF goto Wait bcf PIR1,CCP1IF; reset special event trigger bit incf ........etc HTH Mike. Mike.

23rd November 2007, 11:14 AM	#4
ag501	RE hey i have to design it that way because its part of the specification for my project!!! that snippet you sent is that for the pic16f877a(20MHz clock,200ns intruction cycle)

23rd November 2007, 12:55 PM	#6
ag501	:-( alrite i think i have got the counter to count to the base7 but its the delay of 1.38s im having problem with

23rd November 2007, 03:12 PM	#8
Pommie	Just use the code I posted earlier. Test the bit and increment a counter, once it gets to 138 your 1.38s is up. Mike.

23rd November 2007, 03:21 PM	#9
Mike, K8LH	Mike (Pommie) actually provided a workable 10 msec timer solution. The OP really just needs to add a counter that counts 138 of those timer 'ticks' before incrementing his digit counters. Gosh, how hard could it be? Code: ; ; Wait btfss PIR1,CCP1IF ; 10 msec timeout? goto Wait ; no, branch and wait, else bcf PIR1,CCP1IF ; clear Timer 1 interrupt flag decfsz Timer,F ; has 1380 usecs elapsed? goto Wait ; no, branch, else movlw d'138' ; reset 1380 usec Timer var' movwf Timer ; ; ; increment digit counters here then jump back to the Wait sub' ; Last edited by Mike, K8LH; 23rd November 2007 at 06:01 PM.

23rd November 2007, 04:03 PM	#10
Pommie	Mike, Your absolutely spot on except for the bit that is set. It is PIR1,CCP1IF that gets set rather than the timer1 interrupt flg. Mike.

23rd November 2007, 06:02 PM	#11
Mike, K8LH	Oops! Please pardon me. I corrected my previous post.

26th November 2007, 11:48 AM	#13
ag501	hey hi i was on the PICList website and looking at the delay code generator ... it uses an instruction similar to this goto $+1? what does the $ sign mean?