A simple and basic question

[Ted's]

The code

DEFINE OSC 20
WHILE A <> 0
   Zaehler_Byte = Zaehler_Byte + 1
 WEND

is given.

Assuming that Zaehler_Byte = 60000, how long did the loop take?

[BrianT]

I think the following will happen. At startup all variables are cleared so A = 0. Therefore the While A <> 0 test will fail and the WHILE/WEND block will be skipped.

HTH
BrianT

[Acetronics2]

Hi, ted

Supposing you use Zaeler_BYTE as a Word ( Good question ... indeed ) :

As you increment Zaeler_BYTE , you'll reach an overflow ( and return to Zero ) for Zaeler_BYTE = 65536 ...

so, you'll count from 60 000 to 60535 ...

that makes ??? loops ...



BUT ... as it is Zaeler_BYTE ...

Overflow will occur for Zaeler_BYTE = 256

And you'll count only from 96 ( 60 000 Lower Byte ) to 255 ...

that really makes ??? ... loops

Jawohl ???


Alain

PS: we suppose A is an input state ... and can be 0 or 1 ...

[T.Jackson]

I think what Ted is actually asking is something like this ...

DEFINE OSC 20

WHILE Zaehler_Word <> 60000
   Zaehler_Word = Zaehler_Word + 1
WEND

With a 20MHz osc, how long did it take for Zaehler_Word to reach 60,000?

Trent Jackson

[Acetronics2]

Hi, Trent

Once, the littles things I raised up have been solved ... a little round in MPSIM is the next step ...

To be sure ...

Alain

[T.Jackson]

I think that the question is very "meaningful" and not so easy to accurately answer without going into assembly routines. I say this because you need to know the number of instruction cycles needed for each mnemonic, the time taken for each cycle (around 1uS at 4MHz I think), and finally what OP codes are driving the PBP instructions. You need to have a good understanding of assembly code to be able to work it out, which I don't have, otherwise I'd provide an answer.

Trent Jackson

[Acetronics2]

Hi,

I remember Darrel wrote a little bit of program to measure program parts duration ... a SEARCH through those columns will be welcome.

The second way is to use MPSIM ( part of MPLAB ) with the stopwatch : result is quite perfect !

Alain

[T.Jackson]

@20MHz I'm guessing ~3uS per iteration of the loop.

Trent Jackson

[Ted's]

I do not understand your answers.

What you need to take out of this:

If you loop a variable from zero to 60000 on a pic being driven by a 20Mhz Quartz using the pbp code WHILE without adding a Pauseus XY into the loop, what does this value tell me about the time being elapsed.