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

John,

I run most of my projects at 20 MHz using a Murata resonator.  The directive I tend to use is OSCXT2.

Remember that the faster your oscillator speed, the better resolution (and precision) you'll have when it comes to timing (especially with PAUSEUS).  That said, the compiler does a great job a creating timing loops for the FREQ setting; if there is a problem (like attempting 250K serial with a 4MHz FREQ) the compiler will tell you.

The reason I use 20 MHz most of the time is that it's a common value and a good balance between speed and current consumption.  But every project is unique and processor speed should be considered.  In my March N&V project, for example, I found that it ran perfectly well using the 1 MHz internal oscillator, and even though I'm multiplexing 64 LEDs it ran for two full days on an old 9v battery.

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