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How do I safely share a single LCD display between two stamps? — Parallax Forums

How do I safely share a single LCD display between two stamps?

StampmysterStampmyster Posts: 27
edited 2011-02-19 19:12 in BASIC Stamp
I would like to share a Parallax 2X16 LCD (Back-lit) Display with a BS2 and a BSP40 at the same time.

My concern is how to protect the hardware from any potential damage.

Can I simply tie the data- pins together? Do I need a resistor in series? Should the pins perhaps be pulled high or low?

Perhaps this is a no-brainer to many, but I think it is wise to check first.

Thanks!

Comments

  • Clive WakehamClive Wakeham Posts: 152
    edited 2011-02-19 17:19
    How are you going to stop both Stamps from driving the display at the same time?
    Because you could end up with strange outputs....
  • StampmysterStampmyster Posts: 27
    edited 2011-02-19 18:12
    Yes a valid consideration, but the program allows for only one display to send data at a time, using check_busy loops.

    My concerns are purely wiring-up, at this time.

    Thanks!
  • bot7711bot7711 Posts: 16
    edited 2011-02-19 18:18
    You could make one of them the master controller of the Display say the BSP40. Then the other one, say the BS2, you could use one pin and do a serial out command to talk to the BSP40 controller that is the master of the display? Simply transfer the data received out to the display. I'm not sure how many free I/O pins you have though? Then this way you don't have to worry about the data lines? Just a thought
  • Mike GMike G Posts: 2,702
    edited 2011-02-19 18:54
    Take a look at page 430 in the STAMP pdf manual. It's about the SEROUT command but it explains "open baud mode". It shows you how and why to use pull-up/down resistors while driving communications (one direction) without causing a short.
  • StampmysterStampmyster Posts: 27
    edited 2011-02-19 19:06
    Thanks, interesting thought, however one would still have to protect the pins to do so, and I really want each stamp to operate as independently as possible.

    Seems to me, I may want to, at least, pull each pin high using a 4.7K resistor so as be an open drain. This protects the pin and prevent damage if there was a short to ground? And perhaps use a 220 ohm in series on each data line to protect the pins from each other?

    I just want to prevent damage, and think it's worth the asking.

    Thanks!
  • StampmysterStampmyster Posts: 27
    edited 2011-02-19 19:12
    Thanks Mike G!

    That is exactly what i needed to know...I see the 10K and it is pulled to ground.

    Awesome,

    Thanks!
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