Instant Interrupts - Revisited

[HankMcSpank]

Hi,

If you have a T?CKI pin on your pic you can use that pin to check for black stripes. This is the pin for the external clock signal connected to the internal timer/counter. This way you can get an interupt every black stripe or every 2:nd or once per wheel rotation (or anything else more or less). This is all depending of what you preload the counter with. If you have a 8-bit counter and load FF into it, next clock pulse will overflow the counter and you will get an interupt. If you preload it with FF-(dec 48) it will overflow once every full rotation of the wheel.

If you just want to count the stripes preload it with 0 and off you go....

This way your PIC will do most of the counting by itself and giving you more instruction time for something more useful.

If you use the RA2/INT for the magnetic switch you can use RA5/T1CKI the external clock input for the stripes phototransistor

/me

Thanks...there's some top tips there.

Just a thought here - is it even possible to get reliable results with mechanical switches & interupts?

By this I mean, a mechanical switch normally needs a debounce, else you'd get more than one interupt for every time the switch 'settled'? In my situation, it's importnat that there's just one 'trigger' for every revolution of the encoder wheel (so I can establish how many interupts/black stripes the PIC has counted over one rev)...if I used an interupt for the magnetic switch, there'd be a possibility of not just one interupt...but several in quick succession...which will cause a bit of 'fog' whilst trying to confirm that my wheel, circuit & PIC are all in sync & counting 48 stripes per turn!

By the way...I've now dabbled with Darrel's "Hello World" which will suit my encoder wheel needs perfectly....after wrestling with 'pin' polling for weeks with my encoder wheel & getting very erratic results, I'm one very happy McSpank here today! October 05, 2002 maybe was a good day...but I can say without any shadow of a doubt, for me the 19 May 2009 was a lot better !!

Just a couple of small suggestions for Darrel's website (to save avoid a lot of newbie-esque puzzlement) - on Darrel's very first hello world code page, it might be worth saying that a user will need to establish their own PIC variant's 'INT' pin, along with perhaps a couple of PIC specific examples. (it might be ovbious to you old hands, but looking at the plethora of pins PICs have, it wasn't obvious to me!)

Also, for what it's worth...the 16F690 is perhaps the most common chip that newbies come into contact with at the moment (on account it's bundled with Microchip's very popular PikKit2 starter kit)...I had a problem with Darrel's "Hello World" code when I first compiled ...."error: variable wsave3 position request 416 beyond ram_end 367.", ultimately meaning a line in Darrel's DT_INTS-14.bas file needed commenting out - that might also be worth a mention too? (or at least some mention on a FAQ page?)

Anyway, a hearty thanks to Darrel... without his effort towards making interupts easy with PICBasic , I'm sure I would have left interupts for another day (ie sometime in 2023!)