-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 At 09:37 AM 3/27/00 -0600, John C. Frenzel wrote: >Pic List, >Is the internal osc. of the 12C508/9 stable and accurate enough for RS-232? >It seems to work, but can I depend on it? Microchip says resonators are >too variable for serial work, and so I have always used crystals. Is the >internal osc on these chips stable enough for reliable indoor operation? As discussed before, the total error budget over 10 bits (start, 8 data, stop) is 1/2 bit-time, but the stop bit is a special case, in that it just has to be there. The last edge of the stop bit dosen't even really exist, so I'd calculate the max error allowable as 1/2 bit time in 9 bits. This works out to 5.5% error in timing. Of course that assumes that the receiver is exactly correct, which seems doubtful. 2.75% is a more workable figure. (Let the other guy be at least as sloppy as you are) So in the chip spec, what's the tolerance on the internal osc over the voltage/temp range you anticipate using? If it's looser than 2.75%, then you're questionable. If it's looser than 5.5%, you're not survivable. Realize though, the other guy may have eaten more than half the error budget in his receiver! The other side of this is, hobby or production line? A hobby project can push the envelope a lot harder than a commercial product. I see things "working" in hobby projects all the time that would be a "fire the engineer" in a commercial environment. Isn't serial fun? :) -----BEGIN PGP SIGNATURE----- Version: PGPfreeware 6.5.2 for non-commercial use iQA/AwUBON+ym4FlGDz1l6VWEQJiJgCgiDfY5EM2aYK+S9fONTdJJ+FxgM0An0NE dx/u2hBPCa3DHcAvtAi17EdJ =S7lI -----END PGP SIGNATURE-----