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Multi-Prop Question — Parallax Forums

Multi-Prop Question

idbruceidbruce Posts: 6,197
edited 2010-12-01 22:09 in Propeller 1
Hello All

Just a quick simple question pertaining to a multi-prop project. Is it necessary to disconnect the communication lines between the propeller chips when programing? I doubt that it would be necessary, but I just want to make sure before I screw something up.

Thanks
Bruce

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2010-12-01 20:46
    You didn't say how they're connected. If your Propellers are connected using I/O pins 0 - 27, those I/O pins are all in input (high impedance) mode and they can't become outputs until your program(s) start to run. Safest thing to do is to use a 2.2K resistor in each Prop-to-Prop connection. That will protect against accidental application of 5V logic signals to the I/O pins and against having two pins, both in output mode and each in a different state (high/low). You can use a smaller resistor, like 100 Ohms if you're just concerned about connecting two pins both in opposite output states.
  • idbruceidbruce Posts: 6,197
    edited 2010-12-01 21:21
    Mike

    Thanks for the quick reply.

    The comm lines will be between 0 and 27. In a previous posting, you suggested the 2.2K resistors and I kind of followed you advice. I opted for putting a 1K on each end of the line, for a total of 2K and I am hoping that will be okay.
  • Mike GreenMike Green Posts: 23,101
    edited 2010-12-01 22:09
    There are protective diodes from each I/O pin to Vdd and Vss connected "backwards" so they conduct voltages above Vdd+0.6V and below Vss-0.6V to their respective supply busses. These diodes are rated for a maximum 500uA. The resistors are chosen to keep the current below 500uA if you connect an I/O pin to +5V or -5V. They'll also protect if you connect a high output (3.3V) to a low output (0V).
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