Post by thread:delay loop analysis

Can someone tell me if this loop really is 1000 states ? It appears (in the part), to run about 4x the length. Its intended to be a 1 second delay. I did measure the clock, and its actual value (on pin 15 of a C84) is about 833 Hz or 1.2 mS, but not off by enough to throw this whole thing off. What am I missing in my calculations ? spam_OUThcooperTakeThisOuTes.com ; clock is 1mS ; total delay is 1000 states, or one second DELAY_1S ; 1 second delay MOVLW D'10' MOVWF OUTSIDE LD_INSIDE_1S MOVLW D'19' MOVWF INSIDE REPEAT_1S NOP ; A total of 5 states x 19 = 95 NOP ; plus 5 states overhead = 100 states DECFSZ INSIDE,1 ; decrement inside loop by one GOTO REPEAT_1S ; and continue until zero DECFSZ OUTSIDE,1 ; decrement outside loop by one GOTO LD_INSIDE_1S ; Reload inside loop RETLW 0 ; else return

Dear Mr. Cooper, PIC devices execute instructions using FOsc/4. Does it make more sens now ? Chaipi On Wed, 15 May 1996, Harrison Cooper wrote: {Quote hidden}> Can someone tell me if this loop really is 1000 states ? > It appears (in the part), to run about 4x the length. Its > intended to be a 1 second delay. I did measure the clock, > and its actual value (on pin 15 of a C84) is about 833 Hz > or 1.2 mS, but not off by enough to throw this whole thing > off. What am I missing in my calculations ? > > .....hcooperKILLspam@spam@es.com > > ; clock is 1mS > ; total delay is 1000 states, or one second > > > > DELAY_1S ; 1 second delay > MOVLW D'10' > MOVWF OUTSIDE > LD_INSIDE_1S > MOVLW D'19' > MOVWF INSIDE > REPEAT_1S > NOP ; A total of 5 states x 19 = 95 > NOP ; plus 5 states overhead = 100 states > DECFSZ INSIDE,1 ; decrement inside loop by one > GOTO REPEAT_1S ; and continue until zero > DECFSZ OUTSIDE,1 ; decrement outside loop by one > GOTO LD_INSIDE_1S ; Reload inside loop > RETLW 0 ; else return >

The easy way to test this is to run it in MPSIM. It will tell you exactly how many clocks your code is taking. Dont forget to account for the call, goto, and return taking 2 cycles. It also looks like you did not account for the fact that the goto's are not executed on the last pass thru the loops. This is negligable for the outer loop but significant for the inner loop. BTW Andrew Warren has a quick basic program that does all of the work for you in writting code that takes a specific number of cycles. I don't have his web page address handy but some one else is sure to provide it. Hope this helps. Norm At 08:32 AM 5/15/96 -0600, you wrote: {Quote hidden}>Can someone tell me if this loop really is 1000 states ? >It appears (in the part), to run about 4x the length. Its >intended to be a 1 second delay. I did measure the clock, >and its actual value (on pin 15 of a C84) is about 833 Hz >or 1.2 mS, but not off by enough to throw this whole thing >off. What am I missing in my calculations ? > >hcooperKILLspames.com > >; clock is 1mS >; total delay is 1000 states, or one second > > > >DELAY_1S ; 1 second delay > MOVLW D'10' > MOVWF OUTSIDE >LD_INSIDE_1S > MOVLW D'19' > MOVWF INSIDE >REPEAT_1S > NOP ; A total of 5 states x 19 = 95 > NOP ; plus 5 states overhead = 100 states > DECFSZ INSIDE,1 ; decrement inside loop by one > GOTO REPEAT_1S ; and continue until zero > DECFSZ OUTSIDE,1 ; decrement outside loop by one > GOTO LD_INSIDE_1S ; Reload inside loop > RETLW 0 ; else return > >