High density disks, both 3.5 and 5.25, require a much higher flux level to write. A system designed for DD disks will not be able to write to them reliably. Some folks have tried HD 3.5” disks in an Amiga or Mac for example only to find that it reads for a while but after a few weeks or months it no longer does. You can generally write to lower density disks with a HD drive. The exception being that it is best to write 360K 5.25”disks with a 360K drive as the head on these drives was physically larger and the narrower track written by a higher density drive may not work well on all 360K drives.
My take on the TPDD is that it was designed to be cheap (simple) and portable. Thus, they used a simple 8-bit micro to control everything and not one of the floppy disc controller ASICs that were available at that time. But, they wound up with something that would run on AA batteries and use standard media at the time even if the storage capacity was limited. Jeff Birt From: M100 <m100-boun...@lists.bitchin100.com> On Behalf Of Stephen Adolph Sent: Saturday, March 20, 2021 5:59 AM To: m...@bitchin100.com Subject: Re: [M100] TPDD service manual this is quite interesting, and nice detective work. It would seem like an interesting use case here could be to modify this firmware to make it target a standard 1.44MB floppy disk drive. Maybe it would seem a bit backwards because SD cards are more mainstream, but still interesting to think about. I see you have the disassembly in place. On Fri, Mar 19, 2021 at 8:36 PM Darren Clark <biggran...@gmail.com <mailto:biggran...@gmail.com> > wrote: There are 2 memory modes on that processor, Mode0 which uses the internal RAM and ROM (which is how the PDD is being used), and Mode 1 which addresses external memory and masks the internal ROM. The modes are selected at startup and can't be switched until the chip is reset.
