umrobbin@ccu.umanitoba.ca (02/08/91)
I know this isn't an official Coco forum, but it'll have to do... I need to know how the Coco handles the drive selects. We have here four disk drives, three of which we have connected with no problem, but the fourth drive (i.e. drive 3 under RSDOS) is giving us problems. On my old old drive controller, there are three pins pulled on the drive end of the cable. Two of these are drive selects for drives 1 and 2, but the third is, according to all information I have, the side select line. Long ago someone told me that Cocos used side select for the fourth drive select, but as far as I can tell this isn't true (side select goes active for ALL drives, while selects 0,1,2 all behave correctly). This is also the case for a newer controller we tested. So the only way I can figure out to select the fourth drive is to wire a chip to detect SS active with DS0-DS2 inactive. Is this the way its done? (If so, why on earth is it done this way instead of using the fourth drive select like the other computers in the world?) What is the SS line tied to? If it is tied to a side select output on the controller chip, will a more intelligent DOS (OS9?) be able to handle three double sided drives? Steve Robbins <umrobbin@ccu.umanitoba.ca>
pete@wlbr.imsd.contel.com (Pete Lyall) (02/09/91)
If memory serves, the coco disk select is like this:
You may use a maximum of 3 drives IF any are double sided
You may use a maximum of 4 drives IF they are ALL single sided
The 34 pin bus cable lines associated with drive select are:
Pin 10 - Drive 0 (DS1)
Pin 12 - Drive 1 (DS2)
Pin 14 - Drive 2 (DS3)
Pin 32 - Side Select (SS) -or- Drive 4 for RS drives
This is from memory from several hundred years ago (g) ....
Pete
--
Pete Lyall Contel Corporation
Compuserve: 76703,4230 OS9_Net: (805) 375-1401 (24hr 300/1200/2400)
Internet: pete@wlbr.imsd.contel.com UUCP: {hacgate,jplgodo,voder}!wlbr!pete rh2y+@andrew.cmu.edu (Russell E. Hoffman, II) (02/09/91)
> ... [paraphrase] ... explain the drive select/side select mechanism...
As I best recall it from when I used to hack around on the CoCo, the line
that SS is tied to internally can either be tied to SS, leaving no DS3 (drive
sel. 3), or can be tied to DS3, leaving no SS. In plain words, depending
on how you set a particular register and how you've built your cable, you
can have one of two maximum possible configurations:
1.) 3 double-sided drives (up to 720k each, if they're 80 tracks)
2.) 4 single-sided drives.
It's generally preferable to chose option 1, as this gives you
six total sides, as opposed to four as in option two. As i recall,
OS9 supports option 1, provided you have a straight cable with all
the pins in place, so long as you have the right device driver/descriptor.
Hope that helps,
Russell Hoffman
rh2y+@andrew.cmu.edu
Carnegie Mellon University