On 10/20/2016 04:27 PM, Paul Koning wrote: > I would treat this as an analog problem, putting some op amps and comparators > to work. It doesn't seem to rise to the level where D/A devices are needed. > :-)
Clearly op amps and comparators could do the job, probably really nicely, but it seems like you'd end up with a rather large and expensive bus interface. I've wondered if this might be solvable with just a couple FETs. I'm thinking something like in this schematic. http://pdp10.froghouse.org/qsic/drivers-drivers.pdf The resistor to the base of the driver FET is to limit the slew rate (depending on the gate capacitance of the FET and maybe current limiting from the FPGA). An appropriate FET would have to be found, having the right threshold voltage to meet the receiver spec, also a small enough gate capacitance (one friend suggested that a series resistor on that side too might help with that). > Right. I meant an existing non-MSCP non-RL device. Most other disks have > extremely straightforward register command sets; RK05, RP06, the details > differ but the general approach is very easy. I'd planned to implement an RK first, followed by an RP. I didn't realize the RL was any more complex than those but I'll come asking questions of you if/when I get to that. > Any non-DEC disk would be a problem. Writing drivers is a pain if it's even > possible; for some operating systems like RSTS it flat out isn't supported. Our plan was to first emulate the DEC disk controllers as closely as possible. Well, as closely as people tell us is necessary (like, do we have to insert delays to slow our "disks" down to match the real ones?). Then we'd have options for various extensions like 22-bit addresses and larger disk sizes for those people who were able to take advantage.
