Hi folks - The topic of reading or writing older "odd" disk formats (hard-sectored, GCR, whatever) comes up here pretty often. And often the discussion leads towards the Catweasel floppy interface (currently available commercially, as I understand) or the Compaticard interfaces (not currently being manufactured, as I understand). I've recently "modernized" my foreign format disk reading hardware. The idea of both the "old" version and the "new" versions are very similar to each other, and to what other tools like the Catweasel and the Compaticard do: Data from a floppy disk drive comes as a series of pulses on the read data line. All these circuits (using different means) buffer up to an entire track of data in RAM, and then allow a user program to look at the buffer and analyze the data on its own terms. They also allow control over rudimentary floppy functions such as step in/out, load head/start motor, etc. *I* buffer the pulses on the read data line by simply recording a "1" bit if there was a pulse in a window, and a "0" if there wasn't. I sample at 4MHz, meaning that a complete revolution of a floppy requires most a megabit of RAM. I also buffer information such as index pulse data (essential for decoding many hard-sectored floppy formats.) The bit rate from most standard floppy formats is roughly 500 kHz, meaning my 4 MHz sample rate oversamples by a factor of 8 or so. Yes, it's overkill for many applications, but I want to be sure that all information on the floppy is faithfully represented in the buffer. Besides, many GCR and some MFM variants use half- or even third-fundamental-frequency components (sliding the pulse in the window to encode more data without increasing the clock rate) and oversampling is necessary for these formats. Other buffers (I believe the Catweasel falls in this category) record the times between successive pulses in RAM, instead of the "raw bits". My "previous generation" buffer had a megabit of SRAM and interfaced via a 16-bit-in and 16-bit-out parallel interface (usually to a DR11-style interface on a PDP-11). The megabit of SRAM was made up of a whole bunch of 2k*8 SRAMS, meaning that just the buffer memory required a couple of sizable PC boards. (If you're familiar with the technology, you'll get the idea that "previous generation" buffer was based on chips readily available around 15 years ago.) My "new generation" buffer has the same megabit of SRAM - but now in a single SRAM chip - and interfaces via a PC-clone bidirectional parallel port. Other than the big SRAM chip, the rest of the buffer is just eleven SSI and MSI HCTTL IC's. The eleven chips form the PC-side interface, the floppy-side interface, the timing clocks, the buffer sequencer, and the buffer address (17 bits) counters. So how is my buffer different than, for example, the Catweasel? 1. The Catweasel uses some custom LSI parts, as far as I can figure out. My circuit is much more "hackable", anyone with a TTL databook can figure out what it does and improve on it. Or you can build one yourself from scratch. (Other than the 128K*8 SRAM, all the other parts were literally purchased from the local electronics shop. Heck, most of the chips can be bought at Radio Shack!) Total cost for the chips in my buffer is about $30.00, about half of that in the SRAM chip. 2. The Catweasel uses a proprietary, largely undocumented programming interface. My circuitry is entirely open, and I think it's pretty easy to program. (My first hack at acquiring data with the new buffer was dashed off in about half an hour under QBASIC.) 3. The Catweasel requires a bus slot inside a PC-clone. My new buffer uses a much more general purpose parallel interface. So you can hook it up to a laptop, or even to something that isn't a PC-clone at all. Those are what I see as advantages over the Catweasel. There are also some disadvantages: 4. You can't just go out and buy my buffer, but you can buy Catweasels off the shelf. 5. My buffer is strictly "read-only" as I use it. I think the Catweasel (and Compaticard) both allow writing. Would it be worth writing up my new floppy disk data buffer so that others could improve on it? Would anyone be interested in unstuffed and/or stuffed PCB's? Should I give it a name? (The "Timweasel", anyone? I gotta think of a better name!) -- Tim Shoppa Email: shoppa(a)trailing-edge.com Trailing Edge Technology WWW: http://www.trailing-edge.com/ 7328 Bradley Blvd Voice: 301-767-5917 Bethesda, MD, USA 20817 Fax: 301-767-5927