FOR...NEXT strange counting

[flotulopex]

Hello,

I can't figure out how the FOR...NEXT count works.

First my code, then my question.

...
Duty VAR BYTE
Duty = 0

if duty = 0 then
   FOR Duty = 0 TO 254
      HPWM 1, Duty, 1000
      lcdout Dec Duty 'First read of "Duty"
      PAUSE 5
   NEXT
   lcdout Dec Duty 'Second read of "Duty"
endif
...

At the end of the FOR...NEXT execution, first read of Duty = 254. Right after the "NEXT" command, the second read of the variable Duty = 255.

Why is this!?

[mister_e]

Increse PAUSE 5 to PAUSE 500, it counts perfectly.
Why you have 255 on the second LCDOUT?

1   FOR Duty = 0 TO 254
2      HPWM 1, Duty, 1000
3      lcdout Dec Duty 'First read of "Duty"
4      PAUSE 500
5   NEXT

Incrementation of Duty variable is done @ line #5, The condition to exit the for-next loop is done @ line #1. If >254, exit the loop. 255>254?

[flotulopex]

I'm using this routine to switch ON the backlight of my LCD display, gradually but quite quickly (around 1 second). If I "PAUSE 500", it will takes ages to have the backlight fully on.

As stated in the MicroCode help file, the max "duty" value can be 255. If I want to have the backlight fully ON, I should have 255.

If the condition is "FOR Duty = 0 to 255", Duty will turn back to value 0 (zero) after the "NEXT" since it has been declared as a BYTE variable.

Maybe, the best thing to do is to declare Duty as WORD sized...

Nevertheless, the strange thing is that the Duty variable gets incremented by 1 when it exists the FOR...NEXT cycle.

[Darrel Taylor]

Hi flotul,

It won't matter that the Duty variable ends up at 0 when it wraps around. The HPWM will stay at the last DutyCycle it was set to "Inside" the FOR/Next loop. So you can go the full 0-255.

It appears that you are using the "if duty = 0 then" statement to make the backlight only ramp-up once, when power is applied. Which also means that you have this section of code within the Main Loop of the program.

If you take it out of the main loop and put it up at the top of the program, that section of code will only run once.
<br>

[flotulopex]

I have my LCD-backlight controlled with two buttons; this is why it is in the main loop.

The HPWM command accepts the duty value from 0 to 255.

Actually, when the FOR...NEXT cycle is completed with a count up to 255, the value "wraps" from 255 to 0.

But I track this value to prevent a second press on the same button (it's not nice to see the backlight switched OFF instantaneously and dimm up again when it was already ON - looks like a bug to the user).

To get the HPWM at full range, I would count from 0 to 254 in the FOR...NEXT cycle and, when completed, add one more command to set the duty value to 255. This is not very "clean".

Actually I found another way around. I use REPEAT...UNTIL. Now it works.

I was just suprised to see how the FOR...NEXT cycle affects the count.

[Ioannis]

Since the for-next loop counting from 0 to 255 and the HPWM is inside the loop, where is the problem? At the end HPWM will be at 100% (255), the for-next will wrap to 0 since you have byte variable ant the loop will exit.

Thats how a for-next works in the first place. Always exits when variable will pass the upper limit.

Did I miss anything?

Ioannis