test-drb April 1999

test-drb@ccmp.vtda.org

170 participants
1190 discussions

by allisonp＠world.std.com

Well folks, The 8F is now up and basically healthy. The stuck bit was a bad 74L54 that had a stuck input. Shame the replacement I have is a year older than the machine! I ran one program that will execute on a DECMATE but the result is not visible! ;) / TEST PROGRAM FOR pdp-8f / inchworm view with pannel switch set to Acc (8E/F/M) / 0200 *0200 / start address 0200 7200 START, CLA /CLEAR ACC 0201 1211 TAD WORM /PUT WORM CHARACTER IN ACC 0202 7004 MAIN, RAL / PUSH THE WORM LEFT 0203 7000 DELAY, NOP 0204 7000 NOP 0205 2212 ISZ DELCNT /DELAY 4096 (~20MS) INNER 0206 5203 JMP DELAY 0207 5202 JMP MAIN 0210 7402 HLT 0211 0007 WORM, 0017 / FOUR BIT LONG INCH WORM 0212 0000 DELCNT, 0000 / INSIDE LOOP COUNT 0213 $ Next step is to get the terminal interface in and try it aand also verify all of CORE as all I've checked is most of 00200, page 0 and random words. Allison

25 years, 2 months

Fooling with floppy drives

by steverob＠hotoffice.com

> I recently got a IIci (nice machine!) and it works great, but there seems to be > a drive alignment problem. disks formatted on the cx wont always read right > on the IIci. seems that i have to use one external floppy between both macs > in order to get 800k disks to be read reliably. grrr. > To me, that is the most frustrating problem. I've got drives that only work with certain disks, disks that only work with certain drives, drives that only format certain densities. Grrr... I guess it could be that both components (disk and drive) are slightly out of tolerance. The end result is, I've got a stack of drives and don't really know if they're good or not. I've had some success by just cleaning the slides and positioning mechanisms. The lubricants really attract the dust and will inhibit movement of the heads. I generally like to use alcohol or another common agent to remove the gunk. Blue Rain works great but, is kinda expensive. You have to be careful not to wash all the lubricant out of the servo bushings. Without any lubrication, they can wear out pretty fast. Especially the spindle motors. I generally use a fine machine oil to lubricate the moving parts. You can also use a very thin coat of vasoline. At least it stays where you put it. I've never used the DYSAN alignment disks and would be really interested to learn more about them. How effective are they? What other tools do you need? How much do they cost? Steve Robertson - <steverob(a)hotoffice.com>

25 years, 2 months

Fooling with floppy drives

by edick＠idcomm.com

I'm with you on this one. I didn't make or wish it so. AlI did was state how things are. There ought to be a way to fix these things, but since their cheaper bretheren are available for the PC (throw-away) market, it's hard to get someone to fix them for less than a new one costs. Keep in mind that a guy who fixes them himself can do the job, but even an altruistic fellow indeed would rather spend $25 to replace a drive than spend half a day only to find he can't fix the $#@!! thing. Many of the drives to which I refer have only a switch, a couple of optical interrupters, and a single IC on board. . . . . . maybe a few resistors . . . . . They're just not made to repair. Now, if you save a few, perhaps a board swap can help, but be careful! Those high-density connectors attaching the FLEX to the board aren't made to be cycled more than once. They break! Dick -----Original Message----- From: Sellam Ismail <dastar(a)ncal.verio.com> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Thursday, April 08, 1999 1:49 PM Subject: Re: Fooling with floppy drives >On Thu, 8 Apr 1999, Richard Erlacher wrote: > >> Since new floppy drives cost about $25 including shipment, it's difficult to >> justify repairing them. This is frustrating for people like you who have >> drives for which replacements are not readily available for $20 or so. > >What? What if you don't have $25 laying around, or $25 * 12 = $300 as >Mike says is his current number of broken drives. You don't just go and >pull $25 out of your pocket everytime a drive breaks. The last I checked >money still doesn't grow in the pasture (believe me, I check every >morning). > >> Your experience with sloppy workmanship gives clear indication that $10 per >> hour is not enough to pay a competent technician. The occasional look >> inside should give you good indication of why one who can't spend more than >> 15 minutes' time fixing a $20 drive, can't get the job done. These devices >> must be considered "throw-away" items by now. You've got to learn to >> fix-em-yourself. > >Well, exactly. That's why its called a hobby. > >Sellam Alternate e-mail: dastar(a)siconic.com >--------------------------------------------------------------------------- --- >Don't rub the lamp if you don't want the genie to come out. > > Coming in 1999: Vintage Computer Festival 3.0 > See http://www.vintage.org/vcf for details! > [Last web site update: 04/03/99] >

25 years, 2 months

Request for Assistance: Houston, Texas

by dastar＠ncal.verio.com

Is anywhere here in or near Houston? I need someone to retrieve and ship a rather large set of items (non-computer related) to California for me. I'll make it worth your while of course. Please contact me privately. Thanks! Sellam Alternate e-mail: dastar(a)siconic.com ------------------------------------------------------------------------------ Don't rub the lamp if you don't want the genie to come out. Coming in 1999: Vintage Computer Festival 3.0 See http://www.vintage.org/vcf for details! [Last web site update: 04/03/99]

25 years, 2 months

2901s was Re: Rotting away

by ethan_dicks＠yahoo.com

--- Joe <rigdonj(a)intellistar.net> wrote: > Ethan, > > Can you give me a list of machines that you know of that have 2901s? I > know 2901s are in short supply. I'll try to find some in those old game > machines. Any of the Atari vector machines are likely to have 2901's as the core of a math co-processor to manupulate those vectors faster than the little 6502 ever could. My friend Tony is the Atari vector king; I've never owned one, unfortunately. -ethan _________________________________________________________ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com

25 years, 2 months

stepping machanism of Apple Disk ][ drive (was Re: Heatkit 5

by edick＠idcomm.com

Let's not confuse things here. Today, most disks use either a servo track on an unused surface or they use embedded servo written right in with the data they're storing. That certainly helps with speed control as well as with positioning. They now use voice-coil actuators rather than steppers, and therefore can make quite subtle adjustments in head-stack position depending on what is read. Back in the early days, that wasn't so. In that sense, it's fair to say that Apple was somewhat forward in their thinking. Normally they only thought inward, hence, they did this because it saved them money. FM, MFM, RLL including GCR, are simply modulation schemes. They characterize how the data is actually written on the track, but really aren't involved in decoding the position when a track is being found. The data format, however, customarily has extensive information allowing the system to verify the current position of the head on the medium. A typical sort of format layout would have a sync field, followed by an address mark (a framing-sync character sort-of like the unique word used in HDLC and other protocols) to tell the controller what's next, then a position indicator data field to tell the system the current head and sector information, then a CRC, followed by another sync field containing a write splice (write turn-on gap) followed by a data address mark followed by the data and its CRC and yet another sync field containing yet another write splice(write turn-off gap). There are variations on this theme, but that's basically what's there. The basic format is written in the "low-level" format process while the data fields are written in the "high-level" format. On old drives, the drive's internals don't care about the data. They just transfer it. Newer drives, since they have to fiddle with the data in order to set the data rate, manipulate the heads, buffer the data, correct the errors, etc. care very much about and involve themselves greatly with the media content. Hence, they rely less on hardware specifically in place to yield position information. Floppy drives, AFAIK, don't bother with this, though the ZIP and LS-120 drives may very well do so. They have a track-zero detector, and, normally, that's what's used by the system to find track-00. Apple didn't even use one of those because they could move the heads until it seemed reasonable for one reason or another to assume track zero had been reached, perhaps by reading where they were and then making an adjustment, or perhaps by moving the head in one direction or the other until it had to be at the limit. Then they could step inward until data was encountered, and could be interpreted. Someone else will have to elucidate on that, however, because although I know a fair amount about what they might have done, I don't actually know what they did. How about it Eric? How dit they manage a recal? One interesting thing about the Apple GCR modulation format is that it essentially was a "double-density" technique. It was cleverly implemented in a way which saved on hardware, capitalized on software's ability to exploit the time window normally spent waiting for a transfer, and, especially, didn't wed them to one or another FDC chip maker. Those IC's cost plenty back then. This was at a time when Radio Shack still stayed with single-density, and Apple exceeded their capacity easily. Radio Shack was the only major competitor Apple had. This was a real coup! Dick -----Original Message----- From: Cameron Kaiser <ckaiser(a)oa.ptloma.edu> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Thursday, April 08, 1999 6:32 PM Subject: Re: stepping machanism of Apple Disk ][ drive (was Re: Heatkit 5 >::> How does this work? Do you mean that the disk drive has no internal means >::> of judging whether or not it's on the right track and that this is >::> determined by the contents of the disk? >:: >::Basically, yes. The track and sector are stored in the sector header of >::each sector, among other data. > >In fact, most floppy disk systems work that way. Commodore GCR does that. >So does MFM, doesn't it? > >-- >-------------------------- personal page: http://calvin.ptloma.edu/~spectre/ -- >Cameron Kaiser Database Programmer/Administrative Computing >Point Loma Nazarene University Fax: +1 619 849 2581 >ckaiser(a)ptloma.edu Phone: +1 619 849 2539 >-- FORTUNE: You will feel gypped by this fortune. -----------------------------

25 years, 2 months

Fooling with floppy drives

by mikeford＠netwiz.net

Coincident with all this chatter on floppy drives I have run into a streak of uncooperative drives. I happen to be using macs with 3.5" Sony mechanisms, but my question is somewhat general. What do you do with floppy drives that need repairs? Normally I just put them aside, but after this week I have close to a dozen in the defective box and ZERO (actually a negative number since I need even more) reliable units that aren't already installed in other systems. I have already performed the first aid procedures like cleaning the heads (using a wet cleaning floppy), and disassembly down to the bare mechanism and blowing out the bunnies with canned air. This pile is the hard core rejects, floppy doesn't spin, floppy doesn't eject, which I guess means a drive motor or support electronics is shot. For perspective, Apple still wants like $150 for a new floppy, mail order sources have the same for about $70, and reliable refurbs run the gamut >from a low of about $20 up to $50 or more (used OK drives are $10 to $20. and my last pesky supplier was asking $5 for untested pulls). What I am finding disturbing is that more and more of the drives I see have OBVIOUSLY been swapped from another machine, or show other signs of being opened up by non techs (missing screws or other parts). What are your opinions, practices, or sources? Do any of you fix your floppies? Thanks.

25 years, 2 months

stepping machanism of Apple Disk ][ drive (was Re: Heatkit 5 1/4 floppies)

by edick＠idcomm.com

Well, perhaps you're right about the discussions you recall, Eric. I do recall that there was an effort afoot to use 80-track drives to read some diskettes written with the off-track method used by (Bill Budge?) games, etc, in order to defeat their copy protection. I do recall the comment being made, however, that a while person might defeat that particular copy protection, since the mechanism under discussion was capable of putting a track literally anywhere on the diskette, ( which certainly couldn't have been done with a stepper ) the protection scheme wouldn't hold up. In any case, it's good someone else was paying attention at the time, as it didn't really matter to me, though I found it interesting. It was, after all, over 20 years ago. Dick -----Original Message----- From: Eric Smith <eric(a)brouhaha.com> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Wednesday, April 07, 1999 8:37 PM Subject: stepping machanism of Apple Disk ][ drive (was Re: Heatkit 5 1/4 floppies) >"Richard Erlacher" <edick(a)idcomm.com> wrote: >> (2) - I remember lengthy discussions among those members of the Denver Area >> 6502-Users' Group who were presumably qualified to discuss the intricacies >> of the internals of APPLE's disk I/O routines at a level I neither knew nor >> cared about, beyond the superficial details I gleaned from the several and >> varied sessions discussing that set of details. Now, I attended these >> weekely and typically 4-hour long meetings for several years, and KNOW the >> guys who were hashing out the details of the hardware and software in >> question knew what they were talking about, so I accept that as fact. > >Then, as you'll recall, I was one of the people who spoke at those meetings >regarding the operation of the Disk ][. Armed with information provided by >Wayne Wall, Larry Fish, and Peter Boyle, I delved into the disk system in order >to figure out how to defeat various copy protection schemes, including the >various half-track and quarter-track positioning methods. Larry was involved >in Apparat's efforts to interface standard Teac FD55 series disk drives to >the Apple ][ controller. > >> These fellows >> spent a couple of sessions talking about and demonstrating the screwy means >> by which certain game vendors in the Apple market were "protecting" their >> wares by altering the timing of the positioning routine, thereby making it >> possible to write tracks "off the track" by changing the time delay between >> a known cylinder position and the point at which the specific track was to >> be written. This made it impossible for someone using the stock timing of >> the positioning mechanism to read the diskettes so written. > >No, the postioning that was discussed was the half-track positioning I >described earlier. If you look at the Apple RWTS routines (for either 13- >or 16-sector diskettes), you'll find that the low level postioning routine >actually takes an argument that is two times the track number. > >The only thing about it that was non-obvious was the timing of the >acceleration/decelleration profile used to speed up the seek process. >However, this did not affect the final head position. > >> The scheme with the tristate multiplexers came later, I believe, than the >> one I remember. > >I'm not sure what tristate multiplexers you're referring to. The controller >for the Disk ][ never changed in any non-trivial way. Some later cards for >use with the Unidisk and Duodisk used a 19-pin D-subminiature connector in >place of the pair of 20-pin right angle headers, but the electronics was the >same. Starting with the Apple ][c they used the IWM chip, which was a >slightly fancier single-chip version of the original controller, but the >positioner control method didn't change. > >> Apple had several patents, all of which are there to be >> examined if one wishes. I believe this software-timed positioning scheme >> was among them. > >They had exactly one patent from that era which covers the disk controller. >It describes (among other things) how they use a stepper motor for positioning. > >> I doubt, however, that Wayne Wall would have allowed the waste of >> several sessions of the meetings he so firmly controlled back in those days, >> if the assumptions presented as fact in those discussions had not been >> verified. > >I'm sure he wouldn't have. Which is why there was not any discussion of >using DC motors for head positioning. > >> The helical cam I remember didn't have a groove, but rather, a ridge or > >Regarding mechanical details of the Disk ][ drive I'll readily concede that >you are likely correct, as I never bothered to study the mechanism, only >the electronics and code. > >Cheers, >Eric

25 years, 2 months

Heatkit 5 1/4 floppies

by edick＠idcomm.com

Let me qualify this, first of all, with two bits of fact . . . (1) - I didn't care about the APPLE drives because they didn't work with the type of controller I produced, so if I'm wrong, it's caused little damage so far . . . and (2) - I remember lengthy discussions among those members of the Denver Area 6502-Users' Group who were presumably qualified to discuss the intricacies of the internals of APPLE's disk I/O routines at a level I neither knew nor cared about, beyond the superficial details I gleaned from the several and varied sessions discussing that set of details. Now, I attended these weekely and typically 4-hour long meetings for several years, and KNOW the guys who were hashing out the details of the hardware and software in question knew what they were talking about, so I accept that as fact. If it wasn't true, no harm done, but I doubt that was the case. These fellows spent a couple of sessions talking about and demonstrating the screwy means by which certain game vendors in the Apple market were "protecting" their wares by altering the timing of the positioning routine, thereby making it possible to write tracks "off the track" by changing the time delay between a known cylinder position and the point at which the specific track was to be written. This made it impossible for someone using the stock timing of the positioning mechanism to read the diskettes so written. The scheme with the tristate multiplexers came later, I believe, than the one I remember. Apple had several patents, all of which are there to be examined if one wishes. I believe this software-timed positioning scheme was among them. Having said that, I would point out that, given a software scheme sequenced the stepper, it is just as possible that one could have read the diskettes written a half track off by fiddling with the stepping sequence. I doubt, however, that Wayne Wall would have allowed the waste of several sessions of the meetings he so firmly controlled back in those days, if the assumptions presented as fact in those discussions had not been verified. The helical cam I remember didn't have a groove, but rather, a ridge or "fence" in the shape of a helix, which was tracked by a small, spring-loaded, roller bearing. This worked quite well, but, because of inertia and resonances in the system, required an unduly long period to settle. The somewhat more costly band-actuator positioned drives settled in 3ms, typically, a rate which could be advertised and made a drive look "better," although FDC's for the smaller drives had been designed such that the faster step rate couldn't be exploited without fancy external gyrations involving increasing the oscillator rate, since, previously, the mini-floppies, as they were then called, could seldom step faster than 6ms per track. By the time the IBM PC became available, all the drives you saw were capable of the fast step rate, yet IBM's hardware/software wouldn't readily accomodate it. There were freebie patches published by third parties to speed up the step rate, which caused the drives to quiet down considerably. Dick -----Original Message----- From: Eric Smith <eric(a)brouhaha.com> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Wednesday, April 07, 1999 6:16 PM Subject: Re: Heatkit 5 1/4 floppies >"Richard Erlacher" <edick(a)idcomm.com> wrote: >> Apple drives >> used a form of GCR on their drives, the heads of which were positioned with >> a software timed DC motor, while nearly everyone else used FM or MFM on >> drives which used steppers driving band actuators. > >Correct about GCR, but not about head positioning. If you look at the >schematics of the Disk ][ controller card and that of the drive, both of >which were in the DOS reference manuals up through the early 3.3 manuals >(before the Apple //e shipped), you will see that the controller uses four >outputs of a 74LS259 (or 9334) 8-bit addressable latch to control the four >phases of the head positioning stepper motor. > >IIRC, in the drive the four TTL-level phase signals from the controller >are inputs to a ULN2003 which actually drives the motor phases. > >The stepper motor has an additional stable states halfway between any pair >of adjacent tracks. However, due to the head width, it was not possible to >get twice the number of usable data tracks. But you could use non-standard >track positions as long as they were at least two steps apart. One of the >earliest copy protection schemes was to use track 0, 1.5, 2.5, 3.5, etc. >Of course, the copy programs quickly started supporting half-track >positioning. > >The screwy part of Apple's head positioning system is the absence of a track 0 >sensor. The technique to home the positioner was to step away from track 0 a >few steps (call it N), then step toward track 0 by more than 68+N steps >(the number 96 comes to mind but I could be mistaken). This results in the >famous "Disk ][ mating call" sound. > >In fact, you can actually get quarter-track positioning, but you >have to keep one (two?) of the stepper coils driven to hold the positioner >in place. This can be viewed as a very crude form of microstepping. > >Of course, you can potentially also write data *during* the postitioner >motion. However, this was seldom done even for copy protection, because >the repeatability was poor even on the same drive, and very poor between >drives. > >Because the stepper motor was under software control, the RWTS subroutines >(Read/Write Track & Sector, the low-level disk driver) actually used a >ramped acceleration/deacceleration profile, for faster seek times than >in typical systems which used a fixed track-to-track step time. > >Eric

25 years, 2 months

Apple GCR

by CLASSICCMP＠trailing-edge.com

>Can someone explain how the Apple II GCR worked? I tried deciphering this >several years ago and I could figure it out (the only references I found >were very vague). There's one reference which is extremely non-vague: _Beneath Apple DOS_, by Don Worth and Peter Lechner. In it you'll find wonderful illustrations featuring Sir Isaac Newton and leading you through the wonderfully intertwined world of the Disk ][ state machine, 6502 machine code, and modulation formats. This book is still available new (see my past posts to comp.sys.apple2 for details on how to buy it.) If you're too cheap to buy the book (again, buy the book! It's worth every last cent!), the relevant section of it (minus the cute drawings) is online at http://www.umich.edu/~archive/apple2/misc/hardware/disk.encoding.txt But, again, buy the book! Woz is not my super-hero, but he could do amazing things with a half-dozen TTL chips, that everyone else was doing with a hundred or more... -- Tim Shoppa Email: shoppa(a)trailing-edge.com Trailing Edge Technology WWW: http://www.trailing-edge.com/ 7328 Bradley Blvd Voice: 301-767-5917 Bethesda, MD, USA 20817 Fax: 301-767-5927

25 years, 2 months

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test-drb April 1999