Z80 home brew with FDC

[Allison]

>
>Subject: Re: Z80 home brew with FDC
>   From: Eric Smith <eric at brouhaha.com>
>   Date: Sun, 21 Sep 2008 18:02:25 -0700
>     To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
>
>Alexis wrote:
>> 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.
>

Actually it's pretty decent.  However as you point out if you really 
need the ultimate in relaibility and are throwing crap media with loose 
drives in the system then a PLL may help somewhat.


>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 
>perform better.

yep, now just fine one.

Me I gave up on floppies as even at 1.44Mb they are slow and small.
IDE of CF offer more space and less interface headches.  

Allison