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BS1 - PCI/PCO max length — Parallax Forums

BS1 - PCI/PCO max length

SapphireSapphire Posts: 496
in BASIC Stamp
I'm installing a BS1 in an inaccessible location, and would like to bring out the PCI/PCO pins for future program updates. How long can I make the wires without affecting the operation of the BS1 or the ability to program it? I need about 30 feet.

I notice on the schematic that the PCO line is connected to the EEPROM Vcc pin. Should I install a resistor on the PCO at the BS1 to prevent accidental shorts?

Thanks.

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    Well, the simplest answer would be based on the specifications for the PIC chip used as the interpreter on the BS1. You could look up the datasheet and see if there are any electrical characteristics that define those parameters. That said, long leads on logic level lines usually result in problems from EMI/RFI interference as they essentially become antennae. A few feet can be problematic. 30 feet is really likely to cause some problems.
  • SapphireSapphire Posts: 496
    Chris,

    I remember when I used the "parallel" programming cable for the BS1, it was 6 feet long and worked fine, even with it unplugged from the printer port but left connected to the BS1. In this case, I can use whatever wire I want (shielded, unshielded, twisted, untwisted), and terminate it appropriately. I'd like to minimize the number of components at the remote end, but will try some different lengths of wire before installing it.

    PCI appears to be pulled-up on the BS1, so I wasn't too concerned about that. But PCO appears to be used to power the EEPROM, and a short to ground, or noise as you suggest, could be a real problem.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    The parallel programming cable as you noted was shielded. You could get away with maybe 6-9 feet of shielded cable. But more than that and then you have to deal with loading issues.
  • SapphireSapphire Posts: 496
    Thanks Chris. I will test my setup before installing to make sure it works. I figured loading on PCO would be a problem.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    Sapphire, at 30 feet I can almost guarantee it. But even if you're on the border, you may find that it works sometimes and not others. Let us know how it goes. Empirical testing is often the only way to get the final results.
  • SapphireSapphire Posts: 496
    Chris,

    I just tested a 50 foot spool of 4-conductor telephone wire (unshielded, untwisted) on the PCI/PCO/Vss pins, and...

    It works fine! The BS1 runs, I can download a program, and DEBUG works too.

    Then I added a 1k series resistor on the PCO pin at the BS1 to prevent any accidental shorts, and that works fine too.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    Interesting. I wonder what happens if you get near a source of RFI/EMI emissions? ;)
  • Duane DegnDuane Degn Posts: 10,588
    edited 2015-08-10 22:47
    Chris Savage wrote: »
    I wonder what happens if you get near a source of RFI/EMI emissions?

    I was wondering the same thing.

    It's possible to use RS-485 drivers for applications like these. You need a driver chip on both ends but RS-485 generally does a lot better than TTL over long wires.

    I know when I tried to add a 6' extension on my TTL barcode reader, I had a lot of trouble. It only worked reliably with cables 3' or less.

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    Yeah, it always depends on nearby sources of RFI/EMI radiation. RS-422/RS-485 uses differential drive rather than single-ended like TTL or RS-232 use. RS-232 has the advantage of much higher voltage swings but is still limited in overall range compared to differential drive systems.
  • tomcrawfordtomcrawford Posts: 1,126
    Sapphire wrote: »
    Chris,

    I just tested a 50 foot spool of 4-conductor telephone wire (unshielded, untwisted) on the PCI/PCO/Vss pins, and...

    Is the cable still on the spool? Just asking'
  • SapphireSapphire Posts: 496
    Tom,

    Yes, it's still on the spool. I put some other electronics on top of it with no effect. Going to unwind it and run it over the TV and around the microwave later and see what happens.
  • SapphireSapphire Posts: 496
    Final results: with 65 feet of 6-conductor 22 gauge wire in a shielded cable, unspooled, everything works. No program glitches, and I can re-program the BS1 and use DEBUG remotely. Nice!
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    Sapphire,

    Congrats! I know customers who have had 3-6 feet of wire (unshielded) and had all kinds of trouble. I know at least one was firing solenoids in the vicinity and one was switching high power AC loads. Again, a case of the control signals being too close to the power switching circuits. You just have an ideal environment I guess.
  • PublisonPublison Posts: 12,366
    Sapphire wrote: »
    Final results: with 65 feet of 6-conductor 22 gauge wire in a shielded cable, unspooled, everything works. No program glitches, and I can re-program the BS1 and use DEBUG remotely. Nice!

    That's pretty impressive! Nice wrk.
  • ercoerco Posts: 20,256
    I wonder how well 3 coat hanger wires would work to program a BS1 on a jet on a treadmill 30 feet away.

    http://www.engadget.com/2008/03/03/audiophiles-cant-tell-the-difference-between-monster-cable-and/

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