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Unread 05-10-2005, 10:07
sciguy125 sciguy125 is offline
Electrical Engineer
AKA: Phil Baltar
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Re: 16 bit math on PIC

Quote:
Originally Posted by KenWittlief
when in doubt refer to the Microchip data sheets, and if something weird is happening, check the errata data sheet for the part you are using.
Well, that's the thing, I questioned it enough to think that it was strange, but it seemed plausible enough for me to just accept it. I looked at the datasheet, (mis)read at it as saying that it will only increment up to 127, googled it, and found something to back up the strange claim. That was the only guy that actually gave a solid number as to when it overflows.

As a side not to that, the 12F683 is an 8 pin device with 6 I/Os. 3 of I/Os are multipurpose. If you use the internal clock, you can configure the two oscillator pins to be I/O. And if you don't need a reset pin, you configure that to be an I/O also. In the process of doing that, it occured to me that the chip would start running the program and disable the reset as soon as it's plugged into my JDM programmer. But, in order to put it into program mode, you need to do something with the reset pin (I'm fuzzy on the details though). It crossed my mind that it might not be reprogramable under those conditions, but I didn't pay much attention to it. I figured that the protocol would be smart enough to get around that. Why would they make it impossible to reprogram if I didn't set the code protect bits? Well, apparently, the protocol was changed to occomidate these new style chips. The JDM programmer, however, was designed before this change occured. With that said, I now have 2 chips that can't be reprogrammed with the current incarnation of my programmer. The issue was big enough for me to think that it was strange, but it wasn't so screwed up that I thought it would be a problem.

Now, if you'll excuse me, I think I have some 2N7000's in the garage somewhere to fix my programmmer.
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