How fast is RCFAST?

Jello

Hello, I am wondering about RCFAST.

Documentation says:
0 0 0 RCFAST ~12 MHz Internal No external parts. May range from 8 MHz to 20 MHz.
So By default it is ?MHz.· What is the setting to·make it go 20MHz?
Thanks

boeboy

RCFAST is 12 MHz but it is not persice so it can be any where between 8 and 20MHz

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lets see what this does... KA BOOM (note to self do not cross red and black)

JoeCreate

Considering RCFAST is not "precise", would using RCFAST for 2400 and 9600 baud serial communications be a BAD thing? Like, using FullDuplexSerial on one cog at 2400 (receive only) and another running at 9600 baud (rx+tx). To what extreme would temperature need to fluctuate before serial transmission and reception would be unreliable? It doesn't need precise timing anywhere else so I'd like to not-need to use a crystal, if advised this would be acceptable without imminent failure.

Paul Baker

The reason a range is provided is because process variation can make it fluctuate that much, but for each Propeller it is fixed. The norm is around 12MHz. Because of the variation it is not recommended to use the internal oscillator for asynchronous serial communications unless you measure and declare the oscillation frequency first.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

Mike Green

Paul,
My understanding of the internal oscillators is that they are also much more temperature and supply voltage sensitive than an external crystal or resonator. Has that been characterized at all?

Paul Baker

Chip says they are not as sensitive to temperature as process, haven't tested the supply. Still waiting on the electrician to install the 20A dedicated circuit for the environmental chamber, then I will start doing those tests, I'll be sure to swing the rails too.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.