3.5" floppy drive question(s)

On 11 Oct 2008 at 21:17, Tony Duell wrote: I've got some 5.25" MPI drives with a separate "ready" board that plugs into the main drive electronics board. It's got a 96L02 dual one-shot and some discretes to form a ready circuit. One of the problems with add-on ready circuits on the controller side of the select circuitry is that determinining ready has to involve enough time (3 revs usually) to make sure that spindle's up to speed. Unfortunately, this creates a delay every time one changes drive select. Conditioning the READY off of the motor signal is no guarantee, as some drives disable the motor when there's no diskette in the drive. So leaving drives always selected as you describe is a way around the problem. We were plagued by customers simply changing diskettes whenever they felt like it. Relying on a checksum-after-select scheme such as that used by CP/M and early MS-DOS versions was pretty ugly (and not at all airtight, something that plagued MICROSO~1 no end). While playing with the driver, I noted that the write protect signal was conditioned only on select, not on motor, head-load or ready. Experimenting with some of the other engineers to see how fast one could insert and remove a floppy gave a safe polling interval of about 250 msec, which was barely noticeable in normal system operation and performed only if there were open files on the drive. Some of the single-sided 600 RPM Sony (0A1?) drives were also used in a few CP/M systems, such as the Preis. It was a very noticeable improvement over 5.25" media. Cheers, Chuck