1771 floppy controller questions

Richard Erlacher <edick(a)idcomm.com> wrote (concerning plugging a 1771 in backwards): I discovered a more creative way to destroy a 1771 once. It was on a highly personalised system based on a Dick Smith Super 80 (not System 80!) for which I had built my own disk controller. A friend of mine was attempting to build a colour graphics display, and I had the prototype connected between my system and a TV (via RF). There was a lot of herringbone stuff on the screen, and I wondered whether hash from the computer was getting into the RF modulator through the power supply, so I decided to try filtering it with an inductor, to wit, one winding of an old audio output transformer that I had lying about. It didn't help, so I disconnected it. With the power on. The disk drive head went clunk, and the motor turned on. And stayed on. Permanently. At that point I realised that I had neglected to anticipate the effects of inductive kickback. I couldn't get a 1771 to replace it with at the time, so I got a 1791, which looked like a better part anyway (capable of double density [1]) so I wasn't unhappy about having to make a few changes to the circuitry, such as devising an external data separator. More of a challenge was when I discovered that, of the 4 kinds of data mark supported by the 1771, the 1791 could only read two of them. And, of course, the one I had chosen to use (in my unique home-brewed DOS) was one of the ones no longer supported, so I couldn't read any of my disks! Recovering from that situation was an interesting exercise... Footnotes: [1] I never made use of it, though, since my 2MHz Z80 couldn't keep up with feeding the data buffer fast enough. :-( Greg Ewing, Computer Science Dept, +--------------------------------------+ University of Canterbury, | A citizen of NewZealandCorp, a | Christchurch, New Zealand | wholly-owned subsidiary of USA Inc. | greg(a)cosc.canterbury.ac.nz +--------------------------------------+