On a DUT with an external oscillator, I’ve soldered on to said oscillator in order to provide a clock input to my ChipWhisperer Lite. Because I am using a ChipSHOUTER, I’m also using the CW506 Advanced Breakout Board for the purposes of connecting HS2 to the CS trigger port.
I’ve previously had some issues with this breakout board. It seems that IO voltage translation is stuck at 1.8V. No matter what selectors I use, the outputs on the right side are always 1.8V logic. Since my DUT is 3.3V, I’ve just been using the pins on the left side to do all target communication.
I had been confused for a while why my external oscillator had suddenly stopped working. Finally I wondered if the ChipWhisperer was responsible for the failure. I connected the clock signal in the following ways, measuring resistance across the line and checking the clock at each point:
Clock signal not connected to CW: Clock works
Clock signal connected to CW506 via pin: Clock does not work, resistance 21Ω
Clock signal connected to CW506 via SMA port: Clock does not work, resistance 21Ω
Clock signal connected directly to CW Lite while CW506 is connected: Clock does not work, resistance 21Ω
Clock signal connected directly to CW Lite without CW506 connected: Clock works, resistance over 1000 Ω
This implies to me that the Breakout Board is causing interference on this line, something that it probably should not be doing. But perhaps I’ve configured it catastrophically wrong. Could someone point me in the right direction on how to proceed?
Thanks for the report on this. We’ll look into it.
EDIT: What do you have your IO voltage set as on the CW506? By default, I believe it pulls the voltage from the target side VREF pin, so if you don’t have anything hooked up to that pin, the level shifters will be unpowered.
According to the manual, I can force the use of 3.3V by setting the requisite switch, which I have done. I haven’t connected VREF, I can try that by bridging 3.3V to VREF (since the Breakout Board is also powering my DUT.)
If you’ve got SW1 set to the correct position, you should be all good to go. Your symptoms are very strange though - there’s nothing on the board that generates 1.8V. If you’ve got a multimeter, can you check what voltage VCCIO is at?
Bridging VREF with 3.3V seems to have alleviated the voltage translation issue. Unfortunately I’m still seeing interference from HS1, even after I disabled the disconnect switch on the Breakout Board.
Where are you measuring the resistance between? HS1 to ground definitely shouldn’t be 21Ω, though measuring this with something like a multimeter isn’t really the right method. The switch also shouldn’t do anything if you’re feeding in the signal from the SMA connector, as that connects directly to the voltage translator.
I am indeed measuring this with a multimeter, and I agree that HS1 to ground should definitely not be 21Ω. I am feeding the signal from the pin immediately to the right of the 20-pin connector currently though as aforementioned I tried it in all sorts of scenarios.