In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Peter Van der Zee wrote:

Hi William;

Well, I am prepared to step up to the plate and state that what you are attempting (multi-speed selection using the SX oscillator) using ANY relay will categorically NOT work, PERIOD.

The capacitance tolerance on the SX oscillator pins will be totally swamped by the addition of such a device. You need to find another way. 

That said, having an external oscillator sources and selecting one or another source will work provided the clock signal remains contiguous and has no short (faster than 50 or 75 MHZ) "glitches" as that can upset the instruction pipeline and stall the proper operation.

A continuous wave external variable frequency oscillator will work; this is what the SX key does when you connect it in "RUN: mode, and then carefully move the speed slider. Note that when the slider is moved  quickly, there are discontinuities in the clock signal, and the unit SX will stall.

To come up with a circuit to use the SX's external RC oscillator should be simple, but a switchable 50Mhz-to-slow is much more difficult, and will not work with a relay.

Cheers,

Peter (pjv)

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