How to drive ChipWhisperer Lite's I/O pins with a lower voltage?

Hi there, I got the ChipWhisperer Lite and want to connect the I/O pins to a target that runs on 1.6V. So I built a voltage divider using 200k ohm resistors and drove it with pins 18 (+3.3V) and pin 17 (GND). Then I connected pin 8 (VREF) to the middle of the divider (1.6V), but the I/O pins still delivered 3.3V. After studying the schematics, I desoldered SJ6, soldered three pins to JP5 and connected TVREF with the pin in the middle.

However, as soon as I connect pin 8 (VREF) to the voltage divider, the power of pin 18 dropps to something around 0.2 V.

What am I doing wrong?

VREF isn’t used by CW-lite. Its I/Os are fixed at 3.3V. What you need is this:

Hmmm :thinking:the Specsheet says otherwise:

Yes but we don’t recommend or support this. You would also need to regenerate the FPGA bitfile to modify its I/O pad settings. This is where the “easy to damage the FPGA” part comes in:

JP5 selects the IO voltage for the FPGA bank which connects to the 20-pin target. By default SJ6 selects this to be 3.3V. It is not recommended to change this, as it is easy to damage the FPGA by feeding an out-of-range voltage in.

So again we recommend our CW506 breakout board, which can be configured to set its voltage translators to the voltage provided on that VREF pin.