Z80 home brew with FDC

Z80 home brew with FDC Eric Smith eric at brouhaha.com <mailto:cctalk%40classiccmp.org?Subject=Z80%20home%20brew%20with%20FDC&In-Re ply-To=200809220822.16872.thrashbarg%40kaput.homeunix.org> Sun Sep 21 20:02:25 CDT 2008 * Previous message: Z80 home brew with FDC * Next message: Z80 home brew with FDC * Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] ________________________________ Alexis wrote: 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. flip-flop, drives. 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 perform better. ------REPLY------ Hi, Eric is right about the FDC9229 being mode selectable between 179x and 765 modes. It makes a difference in a number of output frequencies, etc. Check the datasheet. It is at the bitsavers.org URL I posted previously. I can't speak to the PLL issue but Eric is consistent with what I have read and heard previously. You can make data separator replacements from TTL but the FDC9229 data separators are really good and provide more than just data separation. They do a whole host of functions such as FDC clock, data window, variable write precompensation, etc. I recommend them and they are fairly easy to work with. They are not easy to find but they are available if you look enough. Is anyone interested in adding a 765 based FDC to their Z80 home brew computer? This design is mostly done and just needs some road testing and another set of eyes to check it out. The software is kind of crude but working. There are only a couple of modifications left on the hardware. First is to attach the FDC9229 write precompensation pins to the latch and second is to connect the remaining two latch pins to FDC interface pin 2 and 34. The hardware will probably get finished this week some time. The software will probably take a while though. Tonight I read and wrote sectors on the IBM PC 360K 5.25" floppy disk. On the same disk, I formatted some tracks so these functions seem to be working in both DD and HD mode. Also verified with Catweasel that the 1.4M 3.5" floppy disk is generating correct tracks. All the sector header information is checking out right it seems. BTW, when working on this FDC project, I cannot say enough good things about the Catweasel. It is like have having x-ray vision into what is being written to the disk and shows all sorts of hidden stuff. Very helpful when you can check independently what the i8272 is doing compared to what it will tell you it is doing. Thanks! Andrew Lynch