Re: Waking up a serial port

Theo <theom+news@chiark.greenend.org.uk> wrote:

bp@www.zefox.net wrote:

Theo <theom+news@chiark.greenend.org.uk> wrote:

 
I'm not seeing an MCU, although it could be underneath or on another board.

 
It turns out there is an smd package with at least 40 pins on the
perpendicular daughter board at the lower of the photo at
http://www.zefox.net/~bp/ampinvt/2nd_inverter/board_photos/IMG_0007.JPG
It's only about 10 mm square, so any markings are going to be tiny.
 
Unfortunately it's on the side that can't be seen in the photo. It's
mounted diagonally, as one sees on images of SBCs. I've tried to get
a look at the package markings but can't make them out vi a dental
mirror, too much stuff in the way. The packaging is rather tight, so
improving the view won't be easy 8-(
 
Obviously it might help to identify the device. Then again, it might not....
I'll try to figure out how to get a good look. Something like a camera
periscape the size of a pencil would be about right 8-) I'm hesitant to
start taking things apart because the device is still usable, if not
entirely perfect.

 
A rough rule of thumb is if you can see a DRAM package (likely to be a BGA)
and some storage (NOR/NAND/SPI flash) then there's a good chance it's
running Linux and the serial port will give you messages from the bootloader
if nothing else.  If it just has an MCU then it's likely running bare metal
firmware and I'd not expect to see anything out of the UART, although it
wouldn't hurt to probe it and confirm.
 
The fact the power is 5V and not 3.3V does suggest it's more likely to be an
MCU.

I've tried connecting a usb-serial adapter to the Tx pin and watched for
output during power-on, at a variety of baud rates. I really expected to
see something, even if it was garbage. Nothing at all. Then I tried to
use my Owon VDS1022i and couldn't see anything. It's sounding like I'm
barking up an empty tree. Next time there's an opportunity I'll try to
get a better look at the daughterboard. But, not holding much hope....

Thanks to everybody who replied!

bob prohaska