The microstep table is a sine wave, with an amplitude of 60 and a length of 256 steps. Add / subtract an offset of 3 and invert the lower two bits. E.g. a sine value of 7 (000111) results in an entry (7+3) XOR 3 = 001010 XOR 3 = 001001.
In the FAQ manual, you find the according configuration for the TMC428.