It is the SD floppy controller on my TRS-80 EI. It is
very sick...
Any sources for 1771 anywhere. I see lots of 197x available.
Alternatively, a
WD1791/1792/1795 is very close in pinout and command set
compatibility and probably could be made to work with a little tweaking.
My
understanding of these parts is that the 179x series had the data separator
on-chip, while the 177x parts had to have a separate chip for the purpose...
The 1771 as used in the TRS80 was FM only. It CLAIMED to have a builtin
data separator, but those familiar with it consider that claim to be
false, at least to the extent of making a large aftermarket for add-on
data separator adapter boards.
The 179x was both FM AND MFM. BUT,... the 179x could not do some of the
data address marks of the 1771 that TRS-DOS required.
There were enough perceived incompatabilities, that the Percom "Doubler"
(and imitations thereof), instead of replacing the 1771 with a 179x plus
trivial glue, put the 1771 and 179x side by side on an adapter board.
Many of the imitation "Doubler" boards came with a 1771 already installed.
How hard could it be to find one??
--
Grumpy Ol' Fred cisin at
xenosoft.com
