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R&S RTB2004 Snooping

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mikeselectricstuff:

--- Quote from: abyrvalg on September 30, 2020, 06:32:05 am ---Maybe that gpio is on one of those debug connectors? Would be more logical than having it accessible on the front panel (if the mode it triggers requires access to internal UART). Try grounding unknown pins (using some 500 Ohm resistor to stay safe) while observing that gpio reg bit via JTAG?

--- End quote ---
A connector pin or test pad would be my guess as well.

ElectronMan:

--- Quote from: mikeselectricstuff on October 09, 2020, 02:10:27 pm ---
--- Quote from: abyrvalg on September 30, 2020, 06:32:05 am ---Maybe that gpio is on one of those debug connectors? Would be more logical than having it accessible on the front panel (if the mode it triggers requires access to internal UART). Try grounding unknown pins (using some 500 Ohm resistor to stay safe) while observing that gpio reg bit via JTAG?

--- End quote ---
A connector pin or test pad would be my guess as well.

--- End quote ---

It is the second pin down on the UART 4-pin connector from my photo above. I grounded that through a 500Ohm as abyrvalg suggested and I see the GPIO pin register change to low for the pin were were interested in.

Edit:
I tested this. It looks like you need to un-ground it for the debug prompt to come up. So it seems it is supposed to be like holding a button during power-on then releasing it.

Unfortunately, even with my new serial dongle, I am not getting any response from the device when trying to type commands. The bottom connector must be RX, as it is the only one left.  Still investigating that.

KaneTW:
Very cool!

abyrvalg:
Great! If you know UART IO addresses you can try finding Rx the same way as that gpio - setup the PC to send something to the dongle port continuously, touch Rx candidate pins with your dongle’s Tx while observing the UART status/data regs via JTAG.

ElectronMan:

--- Quote from: abyrvalg on October 09, 2020, 07:59:38 pm ---Great! If you know UART IO addresses you can try finding Rx the same way as that gpio - setup the PC to send something to the dongle port continuously, touch Rx candidate pins with your dongle’s Tx while observing the UART status/data regs via JTAG.

--- End quote ---

I finally figured it out... The Mondeb interface actually uses that same GPIO pin to receive. It provides no echo (so you have to turn on local echo).

You have to send BREAK (usually Alt-B on terminals) at the end of each command. You also need to hold BREAK while turning it on to trigger the debug terminal.

So from the top of the photo in the original post, the pins on the 4-pin debug connector are:
1 - GND
2 - UART RX
3 - UART TX
4 - VCC?

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