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Why do wiring differences exist in the Prop Demo Board PS/2 connector vs. the P — Parallax Forums

Why do wiring differences exist in the Prop Demo Board PS/2 connector vs. the P

ElectricAyeElectricAye Posts: 4,561
edited 2010-06-14 20:07 in Propeller 1
I noticed there's a difference in how the PS/2 wiring is done on the Prop Demo Board vs. the PS/2 Breadboard Adapter (Parallax # 28060).
On the Breadboard Adapter, +5 volts is used to "power" the mouse. But on the Prop Demo Board, it shows a +5 connection going to one of the PS/2 pins but then there are also connections made to Vdd, which I presume should be +3.3 volts on the Demo board. Why is there a difference?

www.parallax.com/Portals/0/Downloads/docs/prod/edu/28060-PS2Adapter-v1.0.pdf

www.parallax.com/Portals/0/Downloads/docs/prod/prop/PropDemoDschem.pdf

Thanks,
Mark

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Watching the world pass me by, one photon at a time.

Comments

  • Paul BakerPaul Baker Posts: 6,351
    edited 2010-06-14 18:48
    Hi Mark, both methods will work. The likely reason 3.3V is used for the demo board is to reduce leakage current within the Propeller I/O pins, and the likely reason for the +5V on the adapter is for simplicity of hookup so the user doesnt come to the incorrect conclusion that 2 different voltages are required. You can hook the adapter up like the demo board if you want to since the pullup resistors are external to the adapter.

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    Paul Baker
  • ElectricAyeElectricAye Posts: 4,561
    edited 2010-06-14 19:27
    Paul Baker said...
    ...the likely reason for the +5V on the adapter is for simplicity of hookup so the user doesnt come to the incorrect conclusion that 2 different voltages are required....

    So does that mean if I design my own pcb, I can use only 3.3 volts if I want to? and not bother applying +5 volts to that other pin of the PS/2? If so, that would really help simplify my pcb design.

    Thanks, Paul smile.gif
  • Paul BakerPaul Baker Posts: 6,351
    edited 2010-06-14 20:05
    No unfortunately the +5V is required for the power pin of the PS/2 adapter. Its only the signal lines that you can strap to 3.3V or 5V.

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    Paul Baker
  • ElectricAyeElectricAye Posts: 4,561
    edited 2010-06-14 20:07
    Paul Baker said...
    No unfortunately the +5V is required for the power pin of the PS/2 adapter. Its only the signal lines that you can strap to 3.3V or 5V.

    Okay. That's good to know.

    Thanks again! Much appreciated!

    smile.gifsmile.gifsmile.gif
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