AM3358: UART0 is receiving characters when there is nothing connected to it

Hello Jack,

Thank you for the query.

Can you please provide some information on the board you are using ad the setup

Is this seen on multiple boards ?

Regards,

Sreenivasa

Hi KS,

This is a custom board based upon the Beagle Bone Black revC using the AM3358 processor. I don't know what you mean by the 'setup'. I have seen this on multiple boards.

My board has a SN74LVC2G241DCUR to UART0 for console support. I have a 6-pin header for connection to my host PC via a USB to TTL 3.3V serial cable. When I mention nothing is connected, I mean the USB to TTL cable is unplugged from the 6-pin header.

Is there suppose to be a pull-up or pull-down resistor connected to pin-2 (1A - UART0_RX) of the SN74LVC2G241?

If yes, what ohm and connect to GND or 3.3v?

Thank you,

Hello Jack, 
Thank you for the. I think you have explained the setup.

Would it be possible to share the schematic image specific to UART.

You mention the design is based on Beagle Bone Black revC. Have you had a chance to test the same with Beagle Bone Black revC?

Regards,

Sreenivasa

Hello Jack, 

The below referenced thread could help. Please reference that last part of the thread.

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/858570/am5728-uart0-garbage-characters

Regards,

Sreenivasa

I found this schematic for the BBB revC3. https://github.com/beagleboard/beaglebone-black/blob/master/BBB_SCH.pdf

Page 4/11 shows 100K resistor (R165) connecting B_UART0_RX to ground. I have temporarily added a 100K resistor across pin-1 to pin-4 of the 6-pin header. I have only tested for 24 hours but I am no longer receiving unwanted characters on UART0 while nothing is plugged on to the 6-pin header.

I think adding the resistor has fixed my problem, but only time will tell.

Thank you,