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Two Devices Share Serial Lines — Parallax Forums

Two Devices Share Serial Lines

ry.davidry.david Posts: 63
edited 2009-08-12 04:24 in Propeller 1
I am currently communicating to my Prop using a FT232RL.· I also have a XBee module that I have been playing around with last week.· My end application requires the exact same data to be available over the FT232RL or the XBee.· Is it possible to use the same TX/RX lines for both the FT232RL and XBee?

Thanks,
Ryan

Comments

  • ry.davidry.david Posts: 63
    edited 2009-08-12 01:23
    For anyone curious:

    I used the 150-ohm resistors between the FT232RL and prop, and then 1k resistors between prop and my XBee.· I am not sure if 1k is appropriate, but at 57600 baud, everything seems happy.
  • kwinnkwinn Posts: 8,697
    edited 2009-08-12 02:48
    One way communication from the prop to the FT232 and XBee should be fine. If both send data or status back simultaneously you will have a problem.
  • Mike GreenMike Green Posts: 23,101
    edited 2009-08-12 04:24
    You will run into problems on the receive side. The transmit side with the Propeller sending data to both the xBee and FT232RL should be ok. On the receive side, both the xBee and the FT232RL will hold their data line high when idle. The 150 Ohm resistors will prevent damage to either device when one of them starts receiving data and tries to force the Propeller pin low. Unfortunately, you'll then have a voltage divider which will present a voltage of 3.3V / 2 = 1.65V to the Propeller. This is right at the Propeller's switching threshold and you could get anything (high or low) for a value. For this to work properly, you should have an AND gate combining these two signals.
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