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Using P0 port for driving +3.3 V Devices

Narasimha Swamy

Hello,

I have a question. Can we use P0 port of 8051 for I/O of an external device which has +3.3V ratings for its I/O?

Thanks

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  • 0 in reply to Narasimha Swamy

    for most (and I believe the AT89S52 - check the datasheet) old fashioned '51 derivatives P0 is 'open drain' which means that there is no pullup on the pins. Thus if you pull up with resistors connected to 3V3 this will, for output be a 3V3 bus. For input to PO you will have to check the output range (Voh Vol) of your other chip vs the input range of (Vih Vil) the AT chip and beware that you maintain a decent noise margin.

    Erik

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  • 0 in reply to Narasimha Swamy

    for most (and I believe the AT89S52 - check the datasheet) old fashioned '51 derivatives P0 is 'open drain' which means that there is no pullup on the pins. Thus if you pull up with resistors connected to 3V3 this will, for output be a 3V3 bus. For input to PO you will have to check the output range (Voh Vol) of your other chip vs the input range of (Vih Vil) the AT chip and beware that you maintain a decent noise margin.

    Erik

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