dwight elvey wrote: It essentially already has this feature -- it's called HSTMD+Index. The controller waits for the track mark (index pulse between two others), then after it's seen said TM, it waits for the next index pulse. Like this: I I I I I I * ^ Where * is the point where the HSTMD detector triggers, and I is the index pulse. The start and stop detectors are almost identical -- the only difference is which register set the configuration is sourced from. Still, at least I have an upper bound now. 32 sectors it is! -- Phil. classiccmp at philpem.me.uk http://www.philpem.me.uk/

Chuck Guzis wrote: That's easy. The hard-sector support is basically a state machine that bolts onto the start/stop detector. There are four standard trigger modes (immediate, time-delayed, index-pulse and MFM Sync). When the track-mark detector is enabled, an additional state is added to the trigger FSM -- essentially it waits for a single track mark, then carries on waiting for whatever you told it to wait for. So if you program the trigger unit like this: * Start Event = HSTMD + Index Pulse * Start Count = 1 * Stop Event = Index Pulse * Stop Count = 2 What you'll get is this: t i j j I I I I I I I I ... S-----------P S=start, P=stop, -= acquisition zone. t = track mark detected, i = index after track mark, j = index pulses By changing the start and stop counts, you can read any of the 32 sectors individually, or read the entire disc in one shot (the index pulses are stored as part of the timing data, which allows the data to be separated into sectors after it's read). The write module works in a similar way -- it's an FSM that executes single-byte instructions. A byte with a 1 in the MSB waits <byte[6:0]> clock cycles, then writes a transition. A byte with a 0 can execute one of a number of micro-instructions (00nnnnnn is "wait N, don't write", 01000000 is "stop now", and there are a few others for "wait for track mark" and "wait for next index pulse"). The real pain is going to be *testing* all this stuff. I might end up tying a 4046 PLL and a counter to a 3.5" drive to make a "fake hard-sector" drive, just to test the HSTMD... -- Phil. classiccmp at philpem.me.uk http://www.philpem.me.uk/

On 11/19/09, Chuck Guzis <cclist at sydex.com> wrote: I'd like to see it for the possibility of a project that gets bounced around here from time to time - mounting a 12-sector (hard sectored) pack in an RK05, but having a microcontroller emit pulses to the drive electronics that simulate mounting a 16-sector pack - i.e. PDP-11 packs are common (I have dozens myself) and PDP-8 packs are much less common (I have one, and I got that from another list member). It would be *really* handy to be able to lie to the drive about what's installed rather than modify the packs one by one (of course, packs formatted that way would only work in a modified drive - but if you make the mod cheap and easy to build and install, everyone who wants one can build/have one). -ethan