Replace PBP with Assembly concerning Timer0

[selbstdual]

Hello,

I was talking to some representatives of microchip personally and they recommended using the timer0, 1 or 2 to count instead of using a loop like

while x= y
  N = N +1
WEND

due to the timer's resolution.

Using the above example how does the assembly replacement with timer0 or timer2 look like ?

Is this statement of MC true ?

[skimask]

Hello,

I was talking to some representatives of microchip personally and they recommended using the timer0, 1 or 2 to count instead of using a loop like

while x= y
  N = N +1
WEND

due to the timer's resolution.

Using the above example how does the assembly replacement with timer0 or timer2 look like ?

Is this statement of MC true ?

Hey, remember me? I'm still sitting on the table (upside down of course) eating off a folded up chair...
At the risk of sounding like a jerk, I'm going to 'teach you how to fish' rather than serve you a seafood dinner...so here goes...
Select a PIC, any PIC will do, preferably one of the more popular ones these days, read the chapter on a Timer, any timer will do. Let me know when you've got that done.
On another note, I had friday off and I'm in Tucson, Az. for a couple of months, so I took a trip up to Microchip's office's in Chandler yesterday. Who did you talk to? I talked to a bunch of people.

[sougata]

Hi,

It depends on your application. Using any of the timers you can do a counting at the background then depending on the elapsed period you can do other jobs. Normally all the timer registers are accessible through PBP itself. If you need a tight timebase then asm gives you a better control on the actual instruction cycle used. Timer0 may not have a start/stop control. It is clocked from a prescaler or Fosc (external also possible). When timer0 rollsover it sets a hardware interrupt flag TMR0IF. Even if you are not using interrupts you can poll this flag.

Mister_E has done a great utility to make all your timer/pwm/usart calculations a breeze. Find it here http://www.picbasic.co.uk/forum/atta...4&d=1162909841

For your example code something like this can be done in PBP:

' THIS IS MEANT FOR A 18f452 , 16F PICS HAVE DIFFERENT TIMER0 SETTINGS
        X   VAR BYTE       ' SOME VARIABLE
        Y   VAR BYTE       ' SOME VARIABLE

TIMER_ZERO  VAR WORD       ' VARIABLE TO STORE TIMER0

T0CON = %00000111  ' OFF,16BIT,PRESCALE=256

INIT:
TMR0H = 0          ' CLEAR THE HIGH BYTE OF TIMER ZERO (UPDATED WHEN TMR0L IS WRITTEN)
TMR0L = 0          ' CLEAR THE LOW BYTE OF TIMER ZERO

T0CON.0 = 1        ' START TIMER0
MAIN_LOOP:

' DO WHATEVER YOU WANT



IF X != Y THEN MEASURE   ' IF X AND Y DIFFERS THEN GET THE READING

GOTO MAIN_LOOP

MEASURE:
T0CON.0 = 0                       ' STOP TIMER0    
TIMER_ZERO.BYTE0 = TMR0L  ' READ LOW BYTE FIRST (TMR0H IS UPDATED)
TIMER_ZERO.BYTE1 = TMR0H  ' READ HIGH BYTE FIRST 

GOTO INIT                ' DO IT OVER AGAIN

Please note that since you are checking the condition at the end of the loop, anything consuming time inside would give you erronious results. As for the resolution part it is best to keep the loop running and letting the timer count. The lower the prescale value the greater the resolution. But it seems that you would be doing other tasks as well if x and y are not SFRs or PORT registers. Cause your program need to do something with x and y otherwise they will never end the initially matched condition.

It is best that you post your requirements clearly so that friends here can comeup with something useful for you.

[selbstdual]

Dear sougata,

the current code looks like this:

    WHILE CMCON.6 = 0
        Value = Value + 1
    WEND

This is all, there is no interruption. I am using the PIC 16F628A as a minion.

I changed the code to fit my minion, but it can count only to 255 as it is an 8-Bit timer here.

How do I deal with an overflow, means INTCON.T0IF = 1 or INTCON.2 = 1. It should be something like ValueNew = ValueOld + 256.

Current code, not tested

TIMER_ZERO  VAR WORD        ' VARIABLE TO STORE TIMER0

OPTION_REG = %00000111      

INIT:
TMR0 = 0                     'Full register contains t0-value

INTCON.2 = 0                ' START TIMER0/Overflow-Bit = 0
MAIN_LOOP:

    Value = Value + 1



IF CMCON.6 != 0 THEN M   ' IF Komp.output DIFFERS THEN GET THE READING

GOTO MAIN_LOOP

M:
INTCON.2 = 1                      ' STOP TIMER0/Simulate overflow  
TIMER_ZERO = TMR0            'As it is 8-Bit

GOTO INIT                ' DO IT OVER AGAIN

Finally Value should contain TIMER_ZERO's value.

[mister_e]

Hi selbstdual,

what do you need to count exactly? Events, internal clock tick, amount of hair lost in the process?

Well.. what's your current project?

[selbstdual]

Hair ? Is this a joke ? I kept on laughing the whole day. Very funny.

It is about counting the time until CMCON.6 gets a high level.

[Acetronics2]

Just connect pin 2 (C1OUT) to pin 9 or 12 ... and read TMR1H and TMRIL just when needed ...

Details are in that ****ING DATA SHEET... fig 7.1

Alain

PS: No hair lost ... was a pleasure !!!