Old Humax receiver UART debug

MeanMachine

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Hello,

I have a very old Humax receiver with embedded N*S CAS. It is almost about to die and to be phased out. I have opened it just to play around and found 4 pin header which is certainly a UART connector (based on preliminary multimeter tests). I tried to grab a cheap USB to UART cable to see what's being transmitted but nothing shows up on the terminal emulator. It seems the firmware uses non-standard baud rate. Is there any way to figure out what baud rate the TX/RX can be performed? Has there been any typical values used by Humax/N*S in the past?

Any info will be helpful.

Cheers!
 

Spectre

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Hello,

I have a very old Humax receiver with embedded N*S CAS. It is almost about to die and to be phased out. I have opened it just to play around and found 4 pin header which is certainly a UART connector (based on preliminary multimeter tests). I tried to grab a cheap USB to UART cable to see what's being transmitted but nothing shows up on the terminal emulator. It seems the firmware uses non-standard baud rate. Is there any way to figure out what baud rate the TX/RX can be performed? Has there been any typical values used by Humax/N*S in the past?

Any info will be helpful.

Cheers!
Is that a USB to MAX3232 type level converter?
 

Spectre

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It's a USB to UART/RS232/TTL converter cable based on PL2303HXL. It looks like below. Does it make a difference in terms of baud rates?
It won't make a difference baud-wise, I was wondering if it was voltage compatible. That one looks like it is.
 

Spectre

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For a sanity check @MeanMachine, can you try the USB-UART cable on another device that has some sort of UART? Or do you know it definitely works?

If you don't have something to hand you could apply 5V to the power plugs and connect RX and TX to do a loopback test using TerraTerm or similar.

Usually see some garbage with wrong baud.
 

MeanMachine

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Yes, I did a loop-back test following the video below and the cable seems to be working as expected.


When connected to the board, I see some random character sporadically, and also cursor stops blinking on Tera Term for some period of time. But I haven't yet figured out the correct UART configuration parameters.
 

adas

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You won't come in, but I didn't say it's impossible.

Cau Adas
 

lost_sock

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Do you have a logic analyzer? I'm busy digging into an old stb from the local sat provider and managed to figure out the baud rate by hooking up the uart to a logic analyser. I used a salae logic clone I got off aliexpress for a couple bucks, works really well. You can then check the period of the shortest pulse which you can then translate to the baud rate, in my case it was 8.5us which matches closest to 115200. I tried at 115200 and only got garbage out. The next clue to getting the output was signal inversion, the logic analyser was correctly decoding the ascii as non inverted. I had my ftdi dongle incorrectly configured to invert the signal as I thought this was correct for TTL. With the signals not inverted, and a baud rate of 115200 the box spews out it's model number on boot, but that is all, I've tried all the tricks in the book I could find to get to a shell but they've locked this thing down good and proper. RX is most likely disabled in software because I can still measure a few millivolts on the pad, if it was a cut trace it should be completely dead. The challenge continues...
 

adas

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115200 is good, there is no standard approach.

Cau Adas
 

MeanMachine

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Do you have a logic analyzer? I'm busy digging into an old stb from the local sat provider and managed to figure out the baud rate by hooking up the uart to a logic analyser. I used a salae logic clone I got off aliexpress for a couple bucks, works really well. You can then check the period of the shortest pulse which you can then translate to the baud rate, in my case it was 8.5us which matches closest to 115200.
I'm trying this out, but stuck at the first step itself. There is no data from logic analyzer at 8MHz sampling rate. My laptop is struggling to go above that rate, and I did see some data when it could somehow sample at 12MHz or so. Unfortunately I did not save that trace. Now I suspect it might not be RS232 signal at all considering the rate of data transfer. Any ideas as to what it could be?
 

Spectre

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I'm trying this out, but stuck at the first step itself. There is no data from logic analyzer at 8MHz sampling rate. My laptop is struggling to go above that rate, and I did see some data when it could somehow sample at 12MHz or so. Unfortunately I did not save that trace. Now I suspect it might not be RS232 signal at all considering the rate of data transfer. Any ideas as to what it could be?
Does your logic analyser have a state option? With that it is only concerned with state transitions rather than sample rate.

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