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Propeller pin is input--What does another chip see? — Parallax Forums

Propeller pin is input--What does another chip see?

John AbshierJohn Abshier Posts: 1,116
edited 2010-01-28 08:06 in Propeller 1
If a Prop pin is connected to another chip and that pin is set to input by the Propeller, what does the other chip see?· High, Low, indeterminate?

Spin defaults pins to inputs.· Does that occur at the start of the boot process or only after Spin is loaded into cog 0 and execution of the user program starts?

John Abshier

Comments

  • Bill HenningBill Henning Posts: 6,445
    edited 2010-01-27 23:37
    Other chip sees... nothing. When configured for input, the Prop pins are at a very high impedance, so the other chips input would be floating.
    John Abshier said...
    If a Prop pin is connected to another chip and that pin is set to input by the Propeller, what does the other chip see? High, Low, indeterminate?


    Spin defaults pins to inputs. Does that occur at the start of the boot process or only after Spin is loaded into cog 0 and execution of the user program starts?



    John Abshier
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  • BradCBradC Posts: 2,601
    edited 2010-01-28 03:54
    John Abshier said...

    Spin defaults pins to inputs. Does that occur at the start of the boot process or only after Spin is loaded into cog 0 and execution of the user program starts?

    It is the default state on reset. The booter tweaks the direction on 28-31 as required but they revert to inputs as soon as the initial spin cog is loaded as the boot cog is reloaded.

    When stopped, a cog has no influence on the pins, and since at reset all cogs are stopped, by default all pins are inputs.

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  • Nick McClickNick McClick Posts: 1,003
    edited 2010-01-28 08:06
    This is called 'Tri-state' logic - the article on wikipedia does a decent job explaining it (and the benefit).

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