TDO/DI sampled just prior to falling edge
This will clock in bits on TDO/DI from 1 to 8 depending on the Length byte. A length of 0x00 will do 1 bit, and a length of 0x07 will do 8 bits. The data will be shifted up so that the first bit in may not be in bit 7, but from 6 downwards depending on the number of bits to shift (i.e. a length of 1 bit will have the data bit sampled in bit 0 of the byte sent back to the PC). The data will be sampled on the falling edge of the TCK/SK pin.