Davide Munari

Pull up on UART RX pin ?

Discussion created by Davide Munari on Nov 29, 2011
Latest reply on Nov 29, 2011 by kef

Hi everyone,

I have a MS9S12GN16 micro, on which I use the serial interface. 

When the RX pin is configured as a general purpose I/O, it is possible to enable and disable an internal pull-up resistor, and to select whether it's a pull-up or a pull-down .So far, everything's fine.

My question is what happens when I enable the serial interface, with the RE (RECEIVER ENABLE) and TE in the proper register.

Is the pull-up/pull-down still available ? Is there a fixed pull-up whenever I select the serial interface regardless of the register setting ?

The datasheet seems not to highlight this point.


My measure evidences that a fixed pull up is enabled when I turn on the serial, but I am not sure I am doing everything right. My wish is to turn off any pull up/down and leave the pin in HiZ.


Any confirmation would be greatly appreciated.

Thanks and have a nice day.