Can LPC812 invert a UART RX input?

[lpcware]

Content originally posted in LPCWare by matterama on Tue Sep 10 08:44:59 MST 2013
Hi all,

I have an incoming UART stream from a proprietary device that is inverted.  In past designs, we have used a simple inverter to correct this and allow decoding using a standard UART.  The LPC800 series allows inverting of the GPIO pins (such that a "high" reads as a 0).  The manual states that if you configure a GPIO pin as an output, all other special functions are turned off.

What is not exactly clear from the manual (and the configuration tool) is whether the GPIO input functions still apply for the special functions.  Specifically, we were wondering if the RX pin on the UART (say, UART2 on the LPC812) could also be configured to invert the signal before it enters the UART decoder.  This would save us a part.

The configuration tool seems to allow this, but that may just be an accident and we don't have an evaluation board to test on.

Before we commit a design to this without an inverter, we were wondering if anyone out there could confirm or deny this functionality (i.e. RX pin for a UART can be configured to invert the signal before decoding).

Thanks for your help!

[lpcware]

Content originally posted in LPCWare by matterama on Tue Sep 10 12:53:35 MST 2013
Thank you Ken!  The entire original signal (start / stop bits) is actually inverted when we get it, so the UART should be able to correctly interpret them after the flip from what you have indicated.  Thanks again!

[lpcware]

Content originally posted in LPCWare by usb10185 on Tue Sep 10 11:10:36 MST 2013
Hi,

The INV bit (IOCON Bit 6) will invert the incoming signal before it is presented to the UART block. (Note that everything is inverted at this point, it is not aware of Start or Stop bits etc.)

So it looks like you can remove the external inverter from the design.

Thanks,
Ken