Jules Richardson wrote: I just needed a spare time project to help keep me sane. What with all the university work I *should* be doing... :) This is a 3.5" DSHD drive. It works fine on my BBC Micro, which is what's confusing me, because on a breadboard it's not doing anything. It's as if the drive isn't even connected, but continuity checks out fine. Yes, I've seen the SA400 manual, and a few of the Tandon 5.25" drive manuals. What I haven't seen are any manuals that cover 3.5" drives, though I suppose 99% of the interfacing stuff is the same. I did want to get a primitive MFM data-separator working tonight, but I've spent all afternoon scratching my head over this and come up with nothing. Which should still be enough to make my logic analyser display the 'toggling line' image in the input map display instead of 'stuck high'... -- Phil. | (\_/) This is Bunny. Copy and paste Bunny classiccmp at philpem.me.uk | (='.'=) into your signature to help him gain http://www.philpem.me.uk/ | (")_(") world domination.

Jules Richardson wrote: Oh, I'm going to do most of that in software too. I just want to get MFM sync-word detection and maybe pre-decoding working. SWD would be handy for reading Amiga format discs, on the grounds that the data can start anywhere on the track, not just at an index pulse. AIUI, with uPD765-written discs, you'd start reading when the index pulse goes active, read a whole track, then stop reading when it goes active then inactive, i.e.: __ __ INDEX ___| |_____________________| |___ : : : : Start point Stop point This gives you enough overlap (assuming the index sensor is fairly accurate) to be reasonably sure you've got the whole track. Then you look for the sync markers and decode it in software. With Amiga discs, because the data is stored with no index-pulse sync, you look for the MFM codeword 0x4489 which decodes as 0xA1, but isn't a valid MFM encoding (there's a missing clock pulse -- see last paragraph and bottom diagram of <http://en.wikipedia.org/wiki/Modified_Frequency_Modulation>). The whole reason the datasep is needed is to figure out where the data bits lie. To detect the sync word, you shift data bits into a 16-bit shift register according to the transitions (positive *and* negative) of the Data Window line. If there was a pulse on DATA during a Data Window cycle, you clock in a one, else you clock in a zero. Then you add a comparator (basically an AND gate and a bunch of inverters) to signal when the shift register contains 0x4489. You use that signal to trigger the start of an acquisition cycle, then stop shortly after the sync word is detected again. The beauty of the sync word is that because it's not valid MFM (but it's close enough to be picked up by a data separator), it can never appear in normal data, so you don't have to worry about what to do if the track contains a 0xA1 byte somewhere in a sector (or sector header). If you want to be ultra-pedantic, you could search for the whole Amiga sync sequence -- 0xAAAA 0xAAAA 0x4489 0x4489 -- but then you need a 64-bit shift register instead of a 16-bit shift register. I'd love to try my idea out, but I don't have any Amiga floppies to play with, nor do I have an Amiga to create them... -- Phil. | (\_/) This is Bunny. Copy and paste Bunny classiccmp at philpem.me.uk | (='.'=) into your signature to help him gain http://www.philpem.me.uk/ | (")_(") world domination.

http://torlus.com/floppy/

The good thing with open-source CPLD/FPGA projects is that - You can always modify to suit your needs - You can always change the CPLD/FPGA and recompile the code - You can always improve it :o) Greets Alexandre :o)

Jules Richardson wrote: I have a spare A500 (v2.04 ROMs I think), system disks, and DSDD blanks that I'd happily loan or even donate to an active development project. I might even have a mouse to go with it. ;^) The information and sometimes the tools I've picked up here are incredibly valuable to me. Shipping a piece of hardware that I haven't touched in 2 years is a very small contribution, and one I'm glad to make. Doc

Chuck Guzis wrote: Or 5 Hz * 60 seconds = 300RPM. That makes sense. I think I've found the problem though - good ol' drive select issues. Based on the pinout I had, I expected that I'd have to activate /MOTEN_A (pin 10) and /DRVSEL_A (pin 14) to get the drive to spin and output data. That assumption was wrong - the drive wants pin 16 (/MOTEN_B according to my pinout) low, and either /DRVSEL_A or /DRVSEL_B low depending on how the drive is jumpered. This goes back to the 'swap four lines' action the twist in the cable performs. If you want to select drive A, you activate MOTEN_A and DRVSEL_A (pins 10 and 14 respectively), and because drive A is after the twist, as far as it's concerned, MOTEN_B and DRVSEL_B are active (pins 16 and 12 respectively). Because I was raising MOTEN_A and DRVSEL_A, had the drive jumpered for DS0 (drive A), and used a cable with no twist, the drive would get selected (green/amber/whatever activity LED on) but the motor wouldn't spin because MOTEN_x was inactive. Now I'm seeing an index signal on the analyser, and a data signal too. Now for Phase 2 - the MFM data separator. This still doesn't change the fact that I've got a Citizen OSD-U that seems to have issues (the motor spins when the disc is inserted, DRVSEL turns on the LED, but the whole thing goes dead if DRVSEL and MOTEN are enabled with a disc in the drive), but my Panasonic JU257 and the Sony MPF520 are both running fine. I'll probably put the Sony back where it was (I borrowed it from my Acorn BBC Master 128 setup and it's the only drive I've got that can be jumpered to DS0) and use the Panasonic for further tests. Thanks. -- Phil. | (\_/) This is Bunny. Copy and paste Bunny classiccmp at philpem.me.uk | (='.'=) into your signature to help him gain http://www.philpem.me.uk/ | (")_(") world domination.