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Multiple devices to 1 CLK pin? — Parallax Forums

Multiple devices to 1 CLK pin?

N8YXN8YX Posts: 18
edited 2005-11-15 19:51 in BASIC Stamp
I'm fast running out of I/O pins on my BS2p!

There will be several devices attached to the Stamp which require "CLK":

An ADC0831;
A DDS unit;
And a 74HC595 shift register.

Can I tie all these devices' CLK pins together and drive them with one Stamp I/O pin?

Caveats?

Thanks!

...Fred, N8YX...

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-11-15 19:04
    See the Projects Forums, "Binary Digital Clock."· In that I have connected three 74HC595's, DS1302, DS1620 and MAX7219 all to the same Clock and Data lines.· Major I/O pin savings.

    http://forums.parallax.com/showthread.php?p=552892

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Jon WilliamsJon Williams Posts: 6,491
    edited 2005-11-15 19:08
    So long as your DDS unit can ignore clock pulses when it's not selected, you'll be fine.

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    Jon Williams
    Applications Engineer, Parallax
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2005-11-15 19:08
    I'm a firm "believer" in buffering the Stamp's output/s through an external transistor (preferred) or a buffer IC (e.g. 74HC4049 inverter or 74HC4050 buffer.)· Not that·the Stamp is·fragile, but buffering is good insurance [noparse][[/noparse]IMHO].
  • N8YXN8YX Posts: 18
    edited 2005-11-15 19:26
    "So long as your DDS unit can ignore clock pulses when it's not selected, you'll be fine."

    Indeed, it can - a LOAD line must be made "low" to enable a serial data write to the device...

    I'll also buffer the output with a transistor - 2N2222 or similar.

    This will remedy several headaches for me - thanks to all who answered!

    Post Edited (N8YX) : 11/15/2005 7:30:08 PM GMT
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-11-15 19:51
    Remember, in it's default configuration the transistor will typically invert the signal.· Depends on how you connect it, but I don't see any reason to buffer the signals.· If you have bi-directional lines you can use a resistor to prevent issues there.· There is a schematic in that link I sent you if you want to see how the bi-directional devices are handled.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
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