I have built a board for driving some external peripherals which need up to 9V. The CPU (Cortex M0) is powered with 3.3V.
My main power supply is a 9V battery. A step-down converter provides the 3.3V for the CPU (conntected to VBAT and VCC pins).
Unfortunately, I am having some troubles to connect a JTAG interface (ULINK2 with ARM20-pin interface) to the CPU which also provides VCC lines with 3.3V to power the CPU. I'm not sure how I should connect the VCC lines of the JTAG interface.
Do I have to combine these two power supplies (also connect JTAG's VCC to VBAT and VCC)? Will the JTAG interface work if I do not connect VCC at all?