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How fast is RCFAST? — Parallax Forums

How fast is RCFAST?

JelloJello Posts: 9
edited 2007-06-28 17:11 in Propeller 1
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


Comments

  • boeboyboeboy Posts: 301
    edited 2007-04-20 22:06
    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)
  • JoeCreateJoeCreate Posts: 36
    edited 2007-06-28 15:24
    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 BakerPaul Baker Posts: 6,351
    edited 2007-06-28 16:48
    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 GreenMike Green Posts: 23,101
    edited 2007-06-28 16:53
    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 BakerPaul Baker Posts: 6,351
    edited 2007-06-28 17:11
    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.
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