Is VCC and GND of GPIO domain the same as CFF3000 domain?

[zimjjan]

Is VCC and GND on J3 (GPIO domain) the same as on J4 (CFF domain)?
I would assume no, right (should come from, e.g., raspi).
Then, what voltage level is it designed for?

Also, is there a possibility to drive the whole CFF via the Pi's VCC (possibly with a step-down converter)?

[sre]

The purpose of J4 is supplying the CFF with power, so yes VCC on J3 and J4 are the same. With R8 soldered in you should remove the battery from the CFF. Then J3 should be supplied with 3.3V on the Vcc pin. Don't apply 5V, since that can fry the MRF89XA on the CFF (it is only specified for up to 3.6V).