🚀 go-pugleaf

In article <1992Dec23.220244.10435@ee.ubc.ca>, jmorriso@ee.ubc.ca (John Paul Morrison) writes:
>
>The MC68hc705k1 has five methods for setting up oscillation,
>but I can't find accuracies fro two of them. [RC 2 & 3 pin oscillator]

>if it can gaurantee less than 5% error (approx) then it might be useable

There will be temperature and power supply affects on RC osc. frequencies, 
the data book {page 1-8} notes that the 3 pin RC oscillator is more stable
than the 2 pin option.  Table 12.5, page 12-7 notes the worst case freq.
stabilities for the **internal** circuits  EXCLUDING the tolerances of the 
external R & C components.

Your 5% error is not clear as to whether it is absolute, (in which case you
must RC tune or use a crystal or ceramic resonator), or a long term stability 
requirement.  If a stability requirement then your design is limited by the
Vcc stability and the ambient temperature range which the circuit will 
experience.  Low temp coefficient resistors is no problem, however low temp.
coefficient capacitors are not so easy - check your component supplier data
sheets, I can't recall off-hand the type that has the lowest temp. coeff.

For a low production quantity of 20-30 (that you mentioned), probably much
more cost effective to use crystals, as to use RC oscillator should require
considerable effort in testing the frequency stability over the range of
Vcc and temperature [and for a sample of chips!].

If the temp coefficients of the HC705 and the external components can cancel
each other out to some degree then this may be the way to go.

I personally would use Xtal or ceramic resonators where accurate timing was
needed, especially as a preset resistor calibration step is avoided.

PS The data reference is the MC68HC705K1/D book that came with the KICS
K series in circuit simulator kit.

Hope this helps, regards, Bart.