To dramatically increase the scale and spatial resolution for future chronic electrocorticography (ECoG) applications, we propose a wireless brain-machine interface (BMI) system based on a high number (up to 1000) of freely distributed, sub-mm sized (0.25 mm²) IC implants. The chip features an onchip antenna for RF energy harvesting at 900 MHz and data backscattering at 10 Mbps. In order to synchronize and time-multiplex the uplink data transmission of the untethered chips, while allowing their oscillators to free-run to save power, a robust Mbps ASK-PWM downlink data protocol based on digital counters was implemented. To the best of our knowledge, this paper presents the first experimental validation of simultaneous wireless power transfer and bi-directional RF data communications on a network of (32) brain implant ICs over a single inductive coupling link.