08M clock speed tolerance

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Rich36

New Member
I tried to connect a Parallax Serial LCD (#27977) to a picaxe 08M and it doesn't work. The LCD works fine on the BS2. I used an oscilloscope on the outputs of the BS2 and the 08M and found that the 08M took about 5% longer to output a byte of data. This is enough to make the serial data invalid.

My question is: Are the frequencies of the resonators in the 08Ms made within 5% tolerance of each other? If I tried another 08M could it possibly work? Does anyone have any insight?

Thanks,
Rich
 
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Dippy

Moderator
I can't say for sure in your case, but if you suspect an issue like that then check the calibfreq in the Basic Manual.

The PIC on-board oscillators are never as accurate or stable as a (good) external crystal. That's not to say they are bad.
I have had the occasional problem with 18X talking to PICs/Xtal and had to twiddle.
Similarly, I've (rarley) had to twiddle PIC BRGs to talk to PICAXE.
I think all BSs use crystal or resonator don't they? (not sure, long time since I fiddled with Stamp).
It's worth a try assuming you've got all the other things right like commands, levels,grounds and polarities...?

And it's certainly worth a try before reaching for another PICAXE - which may work straight away, again assuming everything else is correct.
 
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Rich36

New Member
Success!

I read the information from the URL and deceided to try the "calibfreq 2" fix and it worked perfect. The LCD responds to all the commands. Thanks sooo much for the help. It's much appreciated.

Rich
 
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