On 17/04/02 at 23:50 Phoebus Dokos wrote: [Floppy connectors]
> Hmm so two drives can work simultaneously (theoretically?) Surprisingly, yes! In fact, the NEC 765 controller (the same core is used on many PC based controller chips, including ones used on GC/SGC) can do parallel head positioning by using multiple selection (for instance, if drive 1 has to move 40 tracks and drive 2 60 tracks, both drives are selected at the same time for 40 tracks and both move 40 tracks, then drive 2 is selected for the remaining 20) but AFAIK this was never used and does not appear in later incarnations of the same FDC core, especially within highly integrated IO chips. > Wouldn't that affect the data transmission?... IIRC there's no way to > distinguish where the data is coming from on the Shugart I/F Correct. Data would be logically OR-ed (looking at the signals one would expect AND-ed because they are active low, and if any data out is low, then the controller sees low since all data outs on all drives are in parallel and open collector), but the data is actually inverted. For all intents and purposes, data would be corrupt. However, you CAN write data in parallel. In theory, you could do the write portion of format for both (or more) drives at the same time. IIRC newer versions of the 765 controller have encoded select bits in the registers (two, to decode to 4 drives), but the chip itself most certainly has 4 separate outputs. Now, depending on the chip itself, these can be used in different ways (some can even have the usage selected based on control reghisters in the chip). On the chip used on GC/SGC, they can be set independently so any combination is possible in theory. On a more recent IO chip with many functions built-in, due to the limitation on number of pins, usually PC speciffic DS1, DS2 and MOTOR1 MOTOR2 are present, and they can only be set in speciffic patterns. > So theoretically with the right twist you can access the drives even if > they are prejumpered for DS1 right? (which brings me back to these IBM ED > drives we talked about a while ago). Correct. But it's a bit more complex than that. Some drives detect density and signal to the controller and their own internal circuits, some expect the controller to select density for them (using mode pins) and (maybe) pass the density encoding to the controller. Also, there is the disk change signal, which again may or may not be generated by the drive or expected by the controller. This all used to be set using jumpers. Of course, where there were jumpers, you had the problem of figuring out which ones do what, so a lot of trial and error may have been needed to make it work. Now that there are none, the problem is worse because you have no idea what it's set to, and no way to change it on the drive, you can only manipulate signals on the cable. BTW density and/or mode pins (don't remember off the top of my head) are quite non-standradly set to odd pin numbers, which are by the standard, all ground, so using a drive that expects control on them on the QL will always result in whatever density is set by those pins being tied to ground, unless appropriate lines on the cable are cut. AFAIK QL controllers do not have density pins (they expect the drive to take care of itself) and density detect is by trial and error (ditto maximum head positioning speed, hence things like FLP_JIGGLE). Also, some combinations of density as generated by the controller and as expected by the drive based on what it finds from the holes on the disk, will not work. In general HD drives often, and ED drives always require the detect holes on the disk to match the density the controller is trying to use. This is important when formatting disks to a lower density or in a higher density drive. Normally, formatting SD in a DD drive will work just fine because it's just the encoding of data that changes - the data rate does not. Formatting DD in a HD drive without plugging the HD detect hole on the disk may be just luck - for HD the data rate and some other parameters are different. In this case the 'DD' disk (HD formatted to DD) can be read in a HD drive, but is unreliable or completely unreadable in a real DD drive. HD disks formatted to DD need to have the HD detect hole on the disk plugged up to work right. Formatting ED drives as anything but ED without appropriately manipulating the holes on the disk will make them unreadable for sure on non-ED drives, and unreliable on ED drives. This is because ED uses a mechanically different method of recording, so the magnetic patterns on the disk end up being different, although the electrical encoding may be as intended for a lower density. Asside: Phoebus, I would sure like to get the ED drives working because they were made while Christ was still walking this earth so the quality is still there, unlike today's drives made out of recycled chinese metal children's toys... >BTW: Nasta as it getting a little late and I am kinda lazy (what else is >new?) I am telling you here, that when you fix the QubIDE, send it >directly to Dave so he can have it for his testing until he finishes the >project. Unless you and Dave already covered that aspect. This is the first word about it that I've heared but that's OK. I will do as you ask. Nasta
