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Fastest crystal speed that FullDuplexSerial can run at? — Parallax Forums

Fastest crystal speed that FullDuplexSerial can run at?

Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
edited 2010-05-03 16:07 in Propeller 1
Has anyone done any testing to what the fastest "Prop" speed FullDuplexSerial can still operate at 9600 or 19200 bauds?

Thanks
OBC

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Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2010-05-02 18:02
    There shouldn't be any limit other than that of the Propeller itself. FullDuplexSerial simply calculates how many system clocks will occur during a bit cell and calculates any other timing from that. All calculations are done with 32 bits. The only limitation on clock speed is that it has to be fast enough for the Baud requested. I think you can get 115KBps with an 80MHz system clock and this ratio is roughly consistent through the range of Propeller system clock speeds. That would get you roughly 56KBps with a 40MHz clock, 19.2KBps with a 13MHz clock, and 9.6KBps with a 6.5MHz clock.

    If you want exact numbers, you could do a timing analysis of the FullDuplexSerial code. There's not a lot of instructions involved in the main loop.
  • Clock LoopClock Loop Posts: 2,069
    edited 2010-05-03 06:22
    Mike Green said...
    I think you can get 115KBps with an 80MHz system clock and this ratio is roughly consistent through the range of Propeller system clock speeds.

    I was able to get 250kbps over two solid core copper wires between two props that were about 6 inches apart @ 80mhz with the fullduplexserial object. Anything above that seemed fairly unreliable. But to get this, I had to use 10k pull down resistors on both wires.
  • BigFootBigFoot Posts: 259
    edited 2010-05-03 14:34
    Our 80 MHz systems all talk over 115K serial links and they are completely reliable.

    We recently switched over to 100 MHz for our latest PoS terminal and hope to start using 230K baud.
    All of our communication modules are serial, Smart FTDI USB cables, Ethernet, WiFi and long range
    wireless. The change in Propeller power consumption was negligible and the 20% increase in speed
    makes a noticeable difference, especially when writing to the display.

    Russ
  • AribaAriba Posts: 2,690
    edited 2010-05-03 16:07
    To answer the initial question:
    The max. Prop clockfrequency for 9600 baud would be: 41e12 Hz or 41 TeraHertz !
    I venture to doubt that somebody has done tests in this region this so far... smilewinkgrin.gif

    Andy
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