How to find the UART
Here is where the UART pins sits on the back of the motherboard.
(Courtesy of ifixit photo and jamez70's illustration)
The pins from 1-4 are:
RX TX GND GND (where #4 is marked)
From probing, we can detect the 1V8 level signal and the baud rate of 115200.
(Courtesy of jamez70)
If you want to hook this up, I suggest you solder on some wires to the pads and run the wires to the front, making life easier to re-assemble the KF.
If you want to construct a simple voltage divider, simply get two resistors and get your soldering gun out. According to Vout = Vin * Rb/(Ra+Rb)
Voltage divider circuit (courtesy of calculatoredge.com)
- Vin: 3V3
- Vout: 1V8
- Ra: 10 kOhm
- Rb: 12 kOhm
If you need more UART details, here are some tips:
- Baud: 115200
- Bits: 8
- Parity: None
- Stop Bits: 1
Looking at the datasheet we get a feeling of all the ball points ("pins") on the CPU. (Observe that this is seen from under the CPU)
OMAP4430 ball bottom layout
By then looking at the UART table TX pin numbers I try to get a feel where they might be located on the chip.
UART 1, 2, 3, 4 table
Finally, I cross referenced the UART table with TX pin and physical position on the board. The colors represent UART 1 TX, UART 2 TX and UART 4 TX. UART 3 doesn't seem likely to be mapped.
UART 1, 2 and 4 TX pin guesses
Observe that these are all estimates, but should narrow the search down (unless they're mapped somewhere way outside of the CPU area that is). I haven't had a chance of testing any of my guesses yet, but I thought I'd at least post my thoughts to get the ball running.