int osc

[teekaytk]

hi all
is it possible to use int osc and rs232 together. i think the intosc clock is not accurate to about 10%. is that right? and if so does that affesct rs232

pls help

thanks

[Ttelmah]

Depends on the int osc, and the temperature.
If you look at (for instance), the 16F628, the internal oscillator, is warranted to be between 3.65, and 4.28MHz, over the entire temperature range, from a 5v supply. This is -9.5 to +7%, and would cause problems. If instead you look at the 18F2420, this has a 'typical' error of +/-1% (at 25C), and a max/min, at the same temperature of +/-2%. Over the entire commercial temperature range, this achieves +/-5%, while going out to the extended temperature range, the error rises to +/-10%. These chips, if operated in a 'reasonable' temperature enviroment (+10 to +40C for example), will maintain acceptable values, with problems appearing over wider temperature ranges. You can in fact read an external temperature sensor, and tweak the oscillator, to compensate for this, and Microchip have a formula, for how the frequency changes with temperature, which does allow figures in the order of +/-3% to be achieved over the entire temperature range if required.

Best Wishes

[teekaytk]

thanks
i am using the pic18f4620 for zigbee. so i think there should nt be a problem then using it at room temp

thanks for your help