Z80 home brew with FDC
eric at brouhaha.com
Sun Sep 21 20:02:25 CDT 2008
> The FDC-1 uses a FD179x controller and it appears it uses the same
> data clock and raw data inputs as the 765.
Not quite. I don't recall the details of the difference, but I think it
may have just been the polarity of one of the signals. The 9229 and
9239 had a configuration input to select between 179x and 765 modes.
The 9216 would directly connect to one, and needed a small amount of
logic (maybe just an inverter) for the other.
> The decoder is made up of a 74LS197 (clock divider), a dual 74LS74 flip-flop,
> both used, a 74LS163 counter and an inverter. There are also some open
> collector NAND gates to select the clock rate for either 8" or 5.25" drives.
> It'll use more individual IC packages, but they're *much* easier to find.
Sure, but it doesn't sound like it's a very good data separator. The
good ones have a PLL (either analog or digital), because it is necessary
to track speed variations, not just of the drive that you're using to
read a disk, but also of the drive that wrote it. Non-PLL data
separators work OK when the disk is both written and read under optimal
conditions, but are unreliable otherwise.
The 9216, 9229 or 9239 are *highly* recommended, as they have a good
digital data separator. The 9229 and 9239 also contain write precomp
logic. The 9239 uses higher resolution timing for its PLL, so it may
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