newbie Q - edge detection?

[Charles Linquis]

Interrupts are the best way, but if you can't use those you can do it as follows:






TopOfLoop:

If Old.Y ^ PortX.Y > 0 THEN
Old.Y = PortX.Y
IF PortX.Y = 1 THEN GOTO DoSomething
ENDIF
GOTO TopOfLoop


DoSomething:



The program loops and tests the port bit against a saved value using
the bitwise exclusive OR. If the saved value is different, then "Old"
is set equal to the port bit. Only when the Port bit has switched from
"0" to "1" will it jump out of the loop.

[sayzer]

If you need to detect say only one or two pins on falling (or rising edge), then you may want to use timers in counter mode. Should work for you.

Then have a check like

IF TMR0=1 THEN 'TMR0 is either on falling or rising edge as you need.
TMR0=0
GOSUB GET_PIZZA
ENDIF

[precision]

Read this

http://www.precision.net.in/picbasic/PIC_INT.PDF

.

[DynamoBen]

I know you're new to PICBasic but you may want to take a look here:

http://ww1.microchip.com/downloads/e...Doc/41214a.pdf

Read through this document and see if anything in there is close to what you were looking for. If so the Capture/Compare/PWM module in the pic is what you will want to use.

[RMCRAVEN]

Many thanks for the varied and detailed replies. I've downloaded the PDFs as recommended and I am trying to make sense of the info therein. I do appreciate the replies and I was hoping to be able to embrace some of the information, but ...

I have a question relating to the learning curve - could someone have a look through the following prose and let me know if I should pack it in or persevere please?

Now is the time for me to admit that I have spent at least 3-4 hours most evenings for the last fortnight trying to compile something that I can understand. So far, all I have managed is to modify an example program to get a couple of buttons to latch a couple of LEDs and a third button to switch them off. I estimate a total of about 30 hours of my effort to get to this stage.

I had a choice of PicBasic or C or ASM and I chose what I hoped would be the easiest. I think I made the right choice but I am also beginning to think that even Basic is beyond me.

I have tried drawing a flowchart of what I need - it helped slightly but the fundamental problem is one of understanding the Basic commands. Here are my observations regarding my own dismal progress:

1) Things like (for example) the BUTTON command don't seem to behave the way I expect them to behave.

2)How on earth anyone ever follows more than one for..next loop, especially nested ones, is beyond me.

3) More than one variable? How do you ever keep track of it in your mind, or even by using loads of diagrams and paperwork?

4) Conditionals such as If..then..else doesn't seem to work - I can see the "if" and "then" parts but the "else" seems to be missing in most examples, or at least the "flow" of the program appears incongruous.

There are a dozen applications for PICs that even I can see should be simple to arrive at (relating to MIDI and aspects of analogue electronic music in particular - trigger generators, clock dividers, interfaces and so on) but the time is approaching for me to throw in the towel.

I had thought that I should see some useful prgoress in two weeks ! Perhaps I should invest in some books - can anyone recommend an ideal title for someone who has ZERO programming skill?

[sayzer]

I will take number 1.

1) Things like (for example) the BUTTON command don't seem to behave the way I expect them to behave.

I never used Button command so far because it is complicated for me too.
Use IF...THEN instead. Much simplier, easier...

But of course this does not remove Button command from the Earth! It will always be there for someone.

[Archilochus]

I'll try 2 & 3...

For CounterA = 1 To 20   ; "CounterA" keeps track of the loop count for the first FOR/NEXT loop

    For CounterB = 1 To 10   ; "CounterB" keeps track of the loop count for the second FOR/NEXT loop
        Pause 1
    Next CounterB
    
    Pause 1
Next CounterA

What happens is...

The first loop begins (call it the "A" loop), and "CounterA" is automatically set to '1' at its start.

The next line of code starts up a second loop (the "B" loop), setting "CounterB" to '1' at the start of that loop.

Since the first "Next" command is the "Next CounterB" line of code, the "B" loop will now continue for 10 iterations until it is finished.

We now hit the "Next CounterA" line - we go back to the beginning of "A" loop, the "CounterA" variable is incremented by 1, and then we restart the "B" loop again, finishing it before again going back to the "A" loop.

The "B" loop runs start to finish each time through the "A" loop. The "B" loop will be run a total of 20 times, for a total of 200 cycles (10 cycles per "B" loop, times 20 "A" loops).

While a FOR/NEXT loop is running, you want to make sure your code does not alter the "Counter" variable that is used to store the loop count (unless you are intentionaly changing it!).
Before a FOR/NEXT loop starts, or once the loop is finished, the variable can be used freely for other purposes in your code.


On #3... Give the variables names that mean something to you - instead of x, y, z, etc, use RedLED, GreenLED (pin variables), EventCount, PumpStatus, etc. Try not to use abbreviations, as you'll forget what they mean after a short time (I always do anyways).


Clear as mud? :-)

Arch

[RMCRAVEN]

Well, those responses were both quick and illuminating! Unfortunately, a couple of hours of experimenting and my loops won't work (the compiler tells me I need an "else" and then tells me that the else isn't associated with a for..next!).

I've spent too long on trying to learn today - time to try again tomorrow. Thanks for everybody's assistance though; I'll press on with it during the week and see if anything begins to sink in.

Cheers

RMC, England

[malc-c]

Sometimes the best way to understand how to structure code is to look at some examples and work your way through it, and then modify it. To give you some idea on how FOR / NEXT loops work:

For (variable) = (start value) to (stop value)
Do something
Next (variable)

so:

led var PORTB.0
i var byte

For i = 1 to 10
high LED
pause 1000
low led
pause 1000
NEXT i

Would turn on an LED on PORTB.0 for 1 second, then turn it off for a second ten times (ie untl i = 10)

If you want to count up in jumps, or count down you use the STEP command

For (variable) = (start value) to (stop value) step (value)

So
For i = 20 to 1 step -1
would effectively count down from 20 to 1 in single digits (ie 19,18,17.... etc)

For i = 1 to 100 step 2
would count give values for i in even values upto 100 (2,4,6,8... etc)

Hope this helps