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SN74CBT3253C: Queries regarding SN74CBT3253C

Alan Varghese
Prodigy 130 points
Part Number: SN74CBT3253C
Other Parts Discussed in Thread: SN74HCS21, SN74HCS08

Hi TI Team,

My requirement is to expand 1 UART lines to 4 seperate UART lines. For that i have choosen the Mux SN74CBT3253CD. The UART lines shall be in 3.3V logic. As per the datsheet the VIH level of the mux is 2-5V and VIL-0 to 0.8. Will that logic level suit my application? Vcc for the mux is set to 5V.  I am AttaQueries ching the Schematics for your reference. Kindly review it and provide your valuable comments.

  • +1
    TI__Genius 10552 points

    Hi Alan,

    Thanks for reaching out about the UART application here! After reviewing the data sheet and your schematic, I don't see any issues with the current layout. VIH and VIL levels of your GPIO inputs S0/S1 look good, decoupling cap is present and a pull up resistor on OE is present. No floating pins so we don't need to touch on that. Looks like you're aware of the logic table here as well so no need for me to go into making sure the states are understood. 

    Let me know if you need anything else here!

    Thanks!
    Alex 

  • 0 in reply to Alex Vish
    Prodigy 130 points

    Thanks for the reply Alex.

    One general doubt is there,

    As per the concept of UART, Both host and the end node can initiate communication. Right?

    If we are using a mux like this, How is it possible to initiate a communication from the end node since the S0,S1 is controlled by the host.

    For example, If the S0 and S1 are provided low in that case  A port= B1 port. Thus, if the end node of B2 need to initiate a communication, How is it possible in this case?

  • +1 in reply to Alan Varghese
    Guru 290750 points

    That is not possible with a mux.

    You could use AND gates (e.g., SN74HCS08 or SN74HCS21) to combine the four RX signals. But this will not work if two nodes try to communicate at the same time.

  • 0 in reply to Clemens Ladisch
    Prodigy 130 points

    Ok.Thanks for the immediate response and your support.