Integrating sx48 protoboard


I put some old code together to have the sx48 act like a rom chip for an old 6502 system. It seems to run as intended in SXSim so I'd like to move to the next step and try to test it on the real hardware.

I'd like some advice on how I would go about integrating the sx48 protoboard into a system to have access to the data & address bus. Can I just tie in the data/address/chip select lines or do I also need to use the 5volts and ground from the other system as well.

Thank you,



  • Hi redbox1

    Welcome to Parallax Forums!

    As with any device that is meant to be connected to a digital system, at least a good ground connection must be present, to ensure proper logic levels being recognized as valid inputs.

    Naturally, this applies to both sides of the link.

    There are exceptions to that rule, but they involve specially crafted transmission/reception circuits, e. g., based on optocouplers, rf links or any other mean that can dismiss the need of a common voltage reference to transmit information.

    The ground connection should be crafted in a way to avoid ground loops, a common plague that are the cause of a lot of headaches, even for the seasoned designer.

    As for the need of a good +5Vdc interconnection, it depends on several factors, mainly based on the nature of the circuits that are being connected.

    The main concerns here are current consumption, noise and link speed.
    As a rule of thumb, good power supply filtering will rule there, thru the use (and proper placement) of a good selection of electrolitic/tantalum and ceramic capacitors.

    A last advice: avoid long lines carrying fast switching signals and try to match bus-grouped signal transmition delays and capacitive loads, as per the affected circuits application notes and datasheets.

    If long runs of wired connections must be made to interconnect the boards, consider the use of twisted pairs (one of the wires being ground, for sure) or, in case of flat cables, use every other lane connected to ground, at least, to minimize crosstalk.
    When doing it this way, pay special attention to ground routing, to don't introduce the curse of a ground loop.
    Avoid using the wires that surround data transmition lines as the solely mean of ground interconnection between boards.

    Hope it helps


  • Thank you Henrique for taking to the time to give such great/informative reply, really appreciate it.

    Looks like I've got a more research/reading to do. I didn't think about the long lines - I'm using 20cm wire but will move it down to 10cm.

    Thank you again!

  • Hi Al

    You're always welcome.

    The informations I'd posted above should not be taken as the final word in the subject, but sure, it carries many lessons learned in the past decades.

    I always hope to help a bit. Good luck!

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