In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Dr Now wrote:

[quote="David B"]I did something similar a few years ago. I wanted to use an 4 mHz ovenized crystal oscillator for my  SX clock, but also wanted to be able to use the in-circuit programmer.

I wired the external oscillator to drive the SX clock input through a resistor, about 4.7K as I remember, and everything worked. The SX worked fine, and I was able to program it with the oscillator in place. 

I asked the question in one of these forums of whether this might be overstressing the SX programmer, and a Parallax engineer said he thought the programmer would have no trouble at all driving the programming against the resistor load.

So maybe you could use an independent external oscillator to drive all the SXes like what I did.

David[/quote]

I tried David's idea to solve a similar problem that's been bugging me for a month.  Before programming with an SX-Key, the oscillator and other chips on that line had to be disconnected before it would work.  It took a bit of experimentation, but if there is a 470 ohm resistor between the oscillator and the SX, everything can stay connected all the time.

Awesome!

JimC

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