>If I use the internal oscillator on the 12C508 with the internal calibration
>value, does anyone know how much to expect the oscillator frequency to
deviate
>from the expected 4MHz value?

I«ve read 5% somewhere, but I can«t find it in the 12C508 datasheet!?
The frequency is also teperature and voltage dependant.

PIC14000 also have internal 4MHz osc:
Internal Oscillator data for PIC14000 from datasheet DS40122B:
"Frequency Range fosc(in) min3.0 typ4.0 max5.0 MHz"
  ** That«s 4MHz +-25%  Ouch!! **
"Temperature Coefficient tc(in) typ -0.04 %/¡C From Tmin to Tmax"
"Supply Sensitivity ss(in) typ 0.8 %/V From VDDmin to VDDmax"
"Jitter jit(in) typ 100 ppm ±3 sigma from mean" - What is sigma?

In a program example from Mchip for the PIC14000 a dealy variable for
software RS232 is calcualted like this:
RS232DLY=23+0.09*Fosc-0.0009*TCFosc*(BTEMP-25)
BTEMP = temperature in one C resolution (calcualted earlier from internal
temp sensor) 
Fosc and TCFosc (frequency at 25¡C) calibration data are required to run this
routine. 
The pic14c000 is shipped without TCFosc data. (temp coefficient of internal
oscillator)
This program example used a fix TCFosc of 10h based on char data.
/Morgan
Morgan Olsson, MORGANS REGLERTEKNIK, Sweden
mrt@iname.com, ph: +46 (0)414 70741; fax 70331
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