Instant Interupts with a 12f675

[Darrel Taylor]

Not Dangerous ... those are interrupts of the third type : When the input turns previous things obsolete !!!

The Dangerous part is showing people how to do it, without a full explanation of what's going on.
The possibilities of disaster are endless for the typical newb around here.

Maybe with a "Code Examples" post giving details of what can go wrong, and how to avoid them ... But just "Here, try this", is going to give people some major heartburn and hair loss.

I do not remember having read something ( T_Save values ... ) could be commented in the ReEnterPBP.bas files ...
Did I miss something from your memories ???

I've mentioned it before for a 12F629.
https://www.picbasic.co.uk/forum/showthread.php?p=23773

It removes the ability to use complex formulas in the ISR.
But typically, the ISR doesn't need them anyhow.

And it's the only way to fit it all in the 629/675.

The 12F683 is really a better choice, with 128 bytes RAM, there's No Problem.
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[wlundonly]

So Darrel,

I'm trying to decide what chip to use and thought maybe you could suggest a chip....there are so many....

Every time I use a new PIC chip I fall in love all over again....

I'm looking for a low-cost, easy to obtain in quantity, chip to use in my timer/controller.

I want the controller to send out a signal containing two 8-bit bytes to an RF transmitter.

The controller could be programed to send the signal out at pre-programed times, say a maximum of 12 times in 24 hours.

The chip would need to comunicate to the user via an LCD.

The chip would also be hooked to an RF receiver and receive a couple of bites from the controlled device, which it would then display on the LCD.

I want it to be easy to program, so I was thinking if I should have a few pins dedicated to the clock and alarm/setting functions.

I haven't really looked into displays yet so I'm not sure how many pins one needs for that. I'm thinking if I used a 14 pin chip I should have plenty of input/output pins.

It is going to be battery powered.

Any suggestions?

Thanks,
Bill

[Darrel Taylor]

<Pre>LCD 6<br>TX/RX radio 2<br>Buttons 3-8 (depending)<br>Crystal 2 (serial comms)<br> ---<br> 13-18 pins</pre>

14-pin devices can only have 12 I/O's at best.

And being battery operated, it might be better to use an LF device.
I think the smallest of those is 18-pin, like the 16LF628A. Works down to 2 volts @ 4mhz.
But they cost a little more.

Like you say, there's a lot to choose from. And it's better to have a few extra pins for whatever comes up, instead of changing to a bigger PIC later.

[wlundonly]

Darrel,

I can't find that part...are you sure about the part number?

Thanks,

Bill

[Darrel Taylor]

It's strange that a search doesn't pull up anything on the microchip site, but it doesn't.

The info for the LF version is in the same datasheet as the F version.

From Digikey ...
http://search.digikey.com/scripts/Dk...words=16LF628A
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[wlundonly]

Thanks Darrel.

I'm going to use the 16LF628A.

Let's see how far I get before I get stumped. LOL