One thing to understand is that the TPDD-2 and TPDD-1 sector access protocols are completely different. The TPDD-1 sector access protocol is documented in the Tandy official software reference manual for the TPDD-1. I've never seen any similar document or information for the TPDD-2.
But as you say there is a BACKUP command so someone could disassemble that to understand the protocol. Might also be interesting to disassemble the program in the TPDD-2 itself if you can get at it. I know there's a way to get the TPDD-1 to execute arbitrary code, if you could get a certain way along with TPDD-2 you might be able to get it to spill its guts, or there might be a readable ROM chip in there. Ken Pettit might have started or completed reverse engineering the TPDD-2 protocol. Ken? And yes you can only use a TPDD or TPDD-2 to access TPDD disks. The format is an oddball. Presumably you could do it with a Catweasel board but no one has proven it. -- John.
