Old Humax receiver UART debug

How many pins is on that connector?

Just trying to rule out it being a JTAG port.

What did you find with the multi-meter? I would expect UART to meter like this...

GND
0v
3.3v (fluctuating)
3.3v (stable)

Spectre said:

Does your logic analyser have a state option? With that it is only concerned with state transitions rather than sample rate.

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I doubt it, at least I couldn't find such an option. It is a cheap knockoff of Saleae Logic. The signal seems to regularly toggle at more than 8MHz, which the logic analyzer cannot capture, resulting in 'framing errors'.

lost_sock said:

What did you find with the multi-meter? I would expect UART to meter like this...

GND
0v
3.3v (fluctuating)
3.3v (stable)

Click to expand...

I get:
GND
0.2V stable
Fluctuating voltage seemingly not exceeding ~2.2V
5V stable

Spectre said:

You could try tracing the pins back to see what they are attached to.

Click to expand...

Made some progress with information gathering. The connector definitely connects to RS232 pins on the microcontroller. Apparently,

The interface levels [need to be?] converted to the levels necessary for the operation of the [microcontroller] by an external converter.

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Now I need to figure out what kind of converter might be required for this and how to build it. Any input is appreciated!

That definitely looks like uart, it's 5v rather than the 3.3v I expected but your adapter will work!

Just to confirm, you had it wired like this?
GND - Black
0.2V - Green
Fluctuating 2.2V - White

Your 8mhz is more than enough, serial is slooooow. Try increasing the duration of capture to 15s, start the capture and power the box, then zoom out and look for any spikes. Are you using the Saleae Logic software to capture? Ctrl+E to export and I'll gladly take a look.

lost_sock said:

Are you using the Saleae Logic software to capture? Ctrl+E to export and I'll gladly take a look.

Click to expand...

Apologies for a long delay in reply. I could not spend time on this for some time. Here is an export in csv format. Can you please take a look?