Pull up on UART RX pin ?

[BV_BV]

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.

[kef]

• 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 ?

Yes

• Is there a fixed pull-up whenever I select the serial interface regardless of the register setting ?

No.

Some pins have pull devices enabled out of reset, some have them disabled. See chapter 1.8 Device Pinouts. Table next to pinout of your device should tell if specific pin has pull device enabled out of reset and what registers are used to control pull device on/off/up/down. If you find that pull device on Rx pin is enabled when RE=1 despite of the state of port S pull device control registers, then I think you should make service request and report it to Freescale.