I wanted to tune the frequencies of 2 microcontrollers with only internal oscillators to get frequencies as close as possible to each other.
The solution is easy. Just tune 1 microcontroller by means of the byte OSCTUNE with bits TUN <5:0>. This can be made visual with software RS232 outputs of both microcontrollers. Compare them e.g. with an oscilloscope *).
By means of an external voltage with ADC the TUN values can be changed. The TUN values are shown on a LCD. If the frequencies are equal the TUN value is known and can be set for that microcontroller.
See the flowcode used in the attached file.
I found a frequency shift possible of +/- 10%.
Kind regards,
Jan Lichtenbelt
*) If you do not have an oscilloscope, it is possible to compare the 2 signals (one inverted) and integrate the output (just an RC circuit) until 0 is reached.
Tunning internal oscillators
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Jan Lichtenbelt
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Tunning internal oscillators
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- Internal_frequency_tuning_V1.fcf
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