AD5933 has real data and imaginary data register (consisting of 2 8 bit register). they store data in 2's complement form(as per datasheet).So does they store 2's complement byte wise? or first they calculate 2's complement of all 16 bit data & store higher byte in one register and lower byte in other?

   What extra circuit I need to use to measure impedance from 1Kohm to 100Kohm with frequency sweep of 1Khz to 100Khz? 

Can you suggest me some references about configuring AD5933?

Thank You