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Newbie Question - Pullup Resistors

noworld

Just getting into electronics and had a question about the ZX Spectrum 2.0 video. About 12 minutes in there are pullup resistors on the data bus. What is the purpose of these resistors? If all the lines are pulled high (1) then how is data put on the bus? Is the specific location of the resistors on the bus important?

 

Thanks!

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  • Hi Nicholas,

     

    Just to add to what has been posted, pull up resisters allow you to stabilize the EM field along the circuit paths.

    As others have pointed out, consistent current switching stabilizes the overall standing wave down the circuit path.

     

    Also, some input circuits are very susceptible to static charge flow if you do not properly ground and terminate the data path.

    Essentially, very bad things happen when static charge exceeds the breakdown voltage for some devices.

     

    When using a parallel bus path, the pull up resistors balance the line into a tuned circuit and keeps the digital data in sync as it moves down the parallel wires.

     

    DAB

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  • Hi Nicholas,

     

    Just to add to what has been posted, pull up resisters allow you to stabilize the EM field along the circuit paths.

    As others have pointed out, consistent current switching stabilizes the overall standing wave down the circuit path.

     

    Also, some input circuits are very susceptible to static charge flow if you do not properly ground and terminate the data path.

    Essentially, very bad things happen when static charge exceeds the breakdown voltage for some devices.

     

    When using a parallel bus path, the pull up resistors balance the line into a tuned circuit and keeps the digital data in sync as it moves down the parallel wires.

     

    DAB

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