TG43 signal and the Nec 765

One of the things done when writing to a Floppy [it's done with all FDC chips if it's done at all!] is to deliberately twook the bit timing based on the bit pattern. The FDC provides a set of control signals (in hardware) and drives a bit of logic to intentionally smear the bits in time to allow for the media effects of close flux transistions. In most cses this is all hardware but usually the amount of precompensation is adjustable by both bit rate and a non FDC control register (back in the 1791/765 days). Some designs further modified the precomp value for the inner tracks (TG43) as drives didn't use TG43 or based on the deigners evaluation of bit crowding on the inner tracks might also alter the precomp timing to optimize flux transistion spacing. This is important as bits written to magnetic media tend to spread themselves out or crowd based on pattern when written closely. Hope this helps. Ok, then I take it that this is in a PC FDC that is based on the 765 core? I ask as a way to point out that features and functions that the base 765 chip have as implemented on an something like a Disk1A are very differnt in a PC. Largely the PC design truncates the interface from the 765 to something simpler abd often far less flexible. Some of the really late chips (post 37C65) do not even fully implement the full complment of interface signals and may only have limited access to things like precomp timing or worse those functions are "wired" by the chips designer to fit their view of what floppies are (IE: antique = 8" floppy, unsupported). Allison