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SN65C3221E: Digital input signals on unpowered IC

Florian Krischker
Prodigy 10 points
Part Number: SN65C3221E

Hello together

Is it possible to supply the RS232 driver from a second board and leave it unpowered at the UART side if the RS232 bus is not connected, or should Schmitt trigger buffers be provided at the digital inputs (ENn and DIN)?

Best regards,

Florian

  • 0
    TI__Mastermind 46607 points

    Hi Florian,

    All the console side facing input pins (/EN , DIN, /FORCEOFF, and FORCEON) need defined logic levels when VCC is active on device or else you could see abnormal operation from device. Essentially is VCC is active no logic input can be left floating. So using buffers to keep the signal low/high on these pins until the UART side is ready would be recommended to avoid issues from design. 

    Please let me know if you have any other questions!

    Best,

    Parker Dodson