On Wed, 12 Feb 2020, William Sudbrink via cctalk wrote:
Interesting daughter board on the 4FDC in this ebay
(sorry if you have to paste the URL back together)
For future reference,
in ebay listings, after the item number is a question mark and the word
"hash". The question mark, and everything that follows it is extraneous
The description, in between "/itm/" and slash item number is optional,
(but often useful), resulting in:
Can you tell what the chip number is on the FDC on the daughterboard?
I have heard that the 4FDC required data separation circuitry on the
DRIVE (Persci?), and that therefore, an unmodified 4FDC could not use
ON TRS80 model 1, and a few other machines, it was found that the stock
"built-in" data separator was inadequate, and a daughterboard was used to
add better data separation. Percom peddled one.
This looks like the Percom Data Separator
If the chip on the board is a 179x or equivalent, then it could be for
replacing a "single density" (FM) chip, such as 1771 with a 179x/8876?.
I have seen an FDCX4, and it looked different from this one.
In the case of the "doubler" boards used on TRS80, there were two
sockets, to add the 179x, but also to keep the 1771, since the 179x could
not produce some of the address marks that TRS-DOS had been using.
Grumpy Ol' Fred cisin at xenosoft.com