"Tomislav Stimac" wrote
I have XR2206 function generator IC. Output frequency is is determined
by capacitor and resistor. Documentation is clear and test circuit
simple. However i cant reach 1 MHz. !! I can't reach above 860 kHz.
Component values are exactly as they need to be for 1MHz.

XR2206 datasheet: Maximum Operating Frequency:
minimum 0.5MHz (that's what the manufacturer guarantees)
typical 1.0MHz (that's what an "average device" will reach with C=1000pF
and R1=1k). This means the spread is not primarily in your R and C but
in the IC itself! If your design _must_ reach 1.0MHz and you don't have
hundreds of ICs to select from, I would not hesitate to reduce R and C by
5...10%. This will increase your f_max by 11...20%.