While analyzing the HVSP for the tx4 and tx5, I noticed some of the commands in the datasheet don't make any sense. Instruction 3 for reading fuses and lock bits is just there to clock out the response, so a no-op instruction works fine for all of them.
Does anyone know why the third SII is different for all of the read fuse bits even though it's seemingly ignored? I even tried all zeros for SDI and SII in the 3rd instruction, and it still works fine.