test-drb April 1999

test-drb@ccmp.vtda.org

170 participants
1190 discussions

homemade computer for fun and experience...

by CLASSICCMP＠trailing-edge.com

>How one place characters on terminal, give examples of terminal >coding as sent from computer to terminal? > >-outputting characters to screen? Say you want to print the character 'W'. You put the letter 'W' into the accumulator, and tell it to output to the serial port. >-resetting cursor to different places? For a truly portable interface, you use a mix of carriage returns, line feeds, and spaces/tabs to put the cursor where you want. If you know you'll have a VT52 or VT100 or ADM3A or (insert generic type of terminal here) you can send a specific character sequence. If you're going to be eventually turning this machine into a CP/M platform, I heavily recommend that you read the copy of your "CP/M Customization Guide" that shipped with your CP/M distribution. You'll find the terminal output/input routines explicitly coded as an example in that book. >Which CPU is very friendly for creating basic codings to put into >ROM and assembling? Z80? or suitable CPU? Just about anything. The Z80 certainly is a popular and easy-to-interface to choice. -- 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, 9 months

Microsoft is about to arrest me!

by geoffrob＠stmarks.pp.catholic.edu.au

---------- > From: Robert Lund <lundo(a)interport.net> > To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> > Subject: Re: Microsoft is about to arrest me! > Date: Friday, April 09, 1999 1:45 > > Oh, god! Does Lord Gates now even have his own police force?? Nothing would surprise me. > Supreme Court battle ahead of you to get out of MS Jail. I thought MS Jail was Windoze 9x/NT? You get in to it then it locks up? Cheers Geoff Roberts VK5KDR Computer Systems Manager Saint Marks College Port Pirie, South Australia geoffrob(a)stmarks.pp.catholic.edu.au

25 years, 9 months

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

by edick＠idcomm.com

The disk drive has a place beyond which its head assembly won't move. If you've ever written FDC code, you know what it sounds like when you try to go beyond the limit. What's more, there's a sensor to tell you when you're at that point, though I doubt Apple used it. It's just as easy to move the heads until you're sure they've gone as far as they can. Once you've done that, what better way could there be than to look for a track and then adjust until the signal is readable? That's how drives of all sorts work today. Of course, they all have some way of establishing where a track ought to be to begin with. Dick -----Original Message----- From: Max Eskin <max82(a)surfree.com> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Wednesday, April 07, 1999 8:53 PM Subject: Re: stepping machanism of Apple Disk ][ drive (was Re: Heatkit 5 1/4 floppies) >On 8 Apr 1999, Eric Smith wrote: >>> 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. > >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? > > --Max Eskin (max82(a)surfree.com) >

25 years, 9 months

Fooling with floppy drives

by SUPRDAVE＠aol.com

In a message dated 08/04/99 15:36:36 Eastern Daylight Time, mikeford(a)netwiz.net writes: << When you say not reading, is it; Fails to spin at all, so all discs are immediately rejected? Doesn't reliably read? My wet cleaning floppy often helps this case. I have a few diagnostic programs, and I think it is TechTool Pro that will do a full drive test, with a 0% to 100% rating that fairly accurately ranks condition of drives. A few of the refurb places sell drives using this rating, with a 90%+ drive fetching a 100% premium over just a working drive. >> well, my mac IIcx had a drive that wouldnot eject disks. the grease had gummed up so i used an aerosol cleaning product and cleaned all that out and used moly grease to fix the stickiness. i also ran a head cleaning disk in the drive for several minutes and amazingly got the drive reading disks again. my IIx will spit disks out ok but refuses to read known good mac formatted floppies. that was cleaned with a head cleaning disk as well but no improvement. unfortunately, the IIx only has one drive instead of two. 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.

25 years, 9 months

homemade computer for fun and experience...

by edick＠idcomm.com

A reasonable example of how to do these things would be available in the IBM PC Technical Reference, since their display boards used the 6845. The scheme is based on the notion of SHARED memory. The processor writes to the video memory, or to the character memory, and the 6845, once initilized, generates the cursor, and scans through memory at the proper rate to effect display of the content. Unfortunately, Motorola unfortunately didn't include a delay stage to allow for translation of ASCII data to video, so an external latch has to be used to delay sync and blanking by a character clock period, which means you might have to accomodate that in your sync timing as well. it means there will be a 1-character period offset between blanking and character video while the graphics will be "right on." -----Original Message----- From: jpero(a)cgocable.net <jpero(a)cgocable.net> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Thursday, April 08, 1999 11:28 PM Subject: Re: homemade computer for fun and experience... >On my homebuilt computer quest....... > >There's two groups: >Built in video and serial i/o to terminal attached concepts. > >Can you explain the process to "init" and operate video chip based >on 6845 chip with own ram ? Possible to use SRAM with it? >Is there CPU specific limitations? > >I have many of them and certainly get put in use on computer. > >And alteratives: > >How one place characters on terminal, give examples of terminal >coding as sent from computer to terminal? > >-outputting characters to screen? >-resetting cursor to different places? > >Which CPU is very friendly for creating basic codings to put into >ROM and assembling? Z80? or suitable CPU? > >Thanks! > >Wizard

25 years, 9 months

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

by edick＠idcomm.com

I think there may be a semantic problem at hand. The single-density (FM) and double-density (MFM) modulation schemes operate on precisely the same density of flux reversals at the media/head boundary. The difference is that the FM imposes a flux reversal between every bit window, while the MFM does not. What this means is that data encoded in MFM can be written to the media at twice the rate as that at which FM is written without taxing the media or read/write channel ordinarily limited to FM. There were some improvements between earlier and later head designs, and media selected for MFM were required to be better because the bits had half as much material in which to be recorded. With MFM, if a clock was missing, which happened half the time a transition was lost, it didn't necessarily make a difference unless the controller happened to be looking for an address mark. So, if your definition of "double density" means twice as many flux reversals per linear inch, well, you're right, I guess, but that's not what the industry meant when the called it double density. I meant the same thing the rest of the folks in the business meant, i.e twice as much data capacity on the same size medium. It's the same with the difference between MFM and RLL hard disk drives. There were a few drives which, as a matter of course, didn't work with RLL encoding. I don't know why this was. I do know that if you use any of a number of translation schemes, of which ANSI GCR is one, you generate a bit stream which, though it uses more than half the channel bandwith to do so, can be recorded at twice the transfer rate as the corresponding NRZ data without allowing excessive accumulation of charge on the heads as would occur if too many ones or zeroes in succession were recorded in NRZ. These schemes don't require the complicated time domain filters and other "neat" circuits commonly used in read/write channels of that time, and provided sufficient densities of transitions to allow clock recovery. The ANSI GCR translates 4 input bits into 5 recorded bits, and recovers them, and ensures that there are enough transitions to allow clock recovery yet no two adjacent cells have transitions. (?) I suppose this is easily achievable with a PROM, and some folks use a state machine to accomplish the same task. I used a prom. It was easy enough to translate 4 bits received at 5 Mb/sec into 10 bits at 8 Mb/sec. A number of code sets have been developed over the years for the purpose of exploiting such "compression" over digitized voice channels, and many other comm channels. Like I said, the Perscis are hangar queens. Like a BMW . . . in the shop a week a month. That's a hyperbole, of course, but it seems that way when you've paid what the things cost back then only to have to pay that much a year again to keep it running. They were fast, though, and hard disks cost a lot more than the Persci drives. Dick -----Original Message----- From: CLASSICCMP(a)trailing-edge.com <CLASSICCMP(a)trailing-edge.com> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Thursday, April 08, 1999 9:03 PM Subject: Re: stepping machanism of Apple Disk ][ drive (was Re: Heatkit 5 >>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. > >Actually, Persci floppy drives in 1976 or so were voice-coil (and quite >a pain to maintain, even then - these days the glue that holds the >optical graticules in place is often failing, and gluing and realigning >from scratch is even harder, even with all the special Persci >realignment jigs and electronic panels.) And a common modification >to these drives (at least for folks like me who specialize in data >recovery) is software-controlled offsets from the normal track positioning, >something that does use the drive's ability to do fine positioning. > >>One interesting thing about the Apple GCR modulation format is that it >>essentially was a "double-density" technique. > >Eric said the same thing, and I disagree with you both. To me (and all >the tech pubs I've read) the density is how many flux transitions you can >do per second (or revolution). GCR is a way of getting more real data with >the same number of flux transitions. Apple GCR drives use single-density >heads and single density data rates, a considerable cost saving factor >in 1977. > >>cost plenty back then. This was at a time when Radio Shack still stayed >>with single-density, and Apple exceeded their capacity easily. > >While using cheap single-density drives! > >-- > 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, 9 months

Heatkit 5 1/4 floppies

by edick＠idcomm.com

I don't feel it necessary to defend what was an obvious memory failure. Eric Smith (much younger than I, and an Apple-owner, unlike me at the time, hence more likely to have paid close attention to the discussion because it affected him and his interests) has already pointed out that I must have been suffering from "old-timer's disease" when coughing up the account of those discussions, though I've corroborated the vague recollection with another old-timer who was there at the time as well, but who also was not an Apple-owner at the time. Since the time of these discussions, I've had occasion to purchase, for a pre-defined purpose, several Apple-II's, some of the wreckage of which and one (maybe more) functional unit of which is serving as a doorstop or spacer between shelves, or some such function. I've nonetheless NEVER looked inside an Apple disk drive, nor have I pondered the schematics beyond noticing that there were such things among the paperwork we got with the half-dozen or so of these units. I never even got particularly familiar with them. I'm certainly not an expert on Apple's hardware, software, or anything else about them. I merely was attempting to recount what I seemed to recall about a specific discussion I witnessed. Clearly the passage of some 20+ years has muddled my recollection. As for the tristate multiplexers, that was an error probably influenced by the fact I'd just plugged a half dozen of them in to three S-100 memory boards I'm giving to some guy in Minnesota who offered me something for them, so I populated them with the requisite IC's, including the 'S257's. I just looked back at the emails I've received in the past month, and couldn't find the specific reference to the part in question, but I must have slipped a couple of numbers in the course of replying to the email in which this subject came up. If they are, indeed, '259's, then they are, as you suggest, addressable latches. Now, I'll hapily accept responsibility for having introduced some error into the discussion of this topic. I guess I'm just going soft in the head. . . That's clearly evidenced in the amount of time I've spent on the discussion of Apple products. Dick -----Original Message----- From: Tony Duell <ard(a)p850ug1.demon.co.uk> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Thursday, April 08, 1999 8:48 PM Subject: Re: Heatkit 5 1/4 floppies >> >> Let me qualify this, first of all, with two bits of fact . . . > >I'll also post some facts. Actually, I'm suprised that nobody else has >done what I've just done, and looked at (a) the Disk II circuit diagrams >and (b) an actual Disk II. Neither are particularly rare. > >> (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 > >If they claimed that the positioner was a normal DC motor and not a >stepper, then I'm afraid they didn't know what they were talking about. > >Every Disk II that I have ever seen (and I've been working on them for >some 20 years or so) has a stepper as the head positioner. The circuits >show this, with a '259 addressable latch on the controller card to >provide the drive signals and a ULN2003 on the 'analog board' to drive >the windings. > >I'll believe that a drive with a DC motor positioner exists when somebody >shows me one in operation, or provides reasonable evidence (schematics, >software to drive it) that it exists. > >> The scheme with the tristate multiplexers came later, I believe, than the > >What tri-state multiplexers? I can't find a tri-state multiplexer in any >part of the Disk II. > >> 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 > >Indeed, and that was done for some copy-protection schemes. >Quarter-tracks might be possible as well... > >> 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 > >The one I have here has a groove. There's a ball bearing in that groove, >with a spring leaf on top of it fixed to the head assembly. As the disk >rotates, the ball bearing tracks along the groove and moves the head. > >-tony >

25 years, 9 months

Oops!

by yakowenk＠cs.unc.edu

Due to some kind of editing error, the Classic Computer Rescue list has just the last few words of an entry from someone in New Hampshire. The same problem exists in my backup copy as of about a week ago, and there is no such entry at all in the backup from several months ago. (Yes, I know, I should keep this in RCS. I should do a lot of things.) If your hunting grounds are Southern New Hampshire ("about an hour north of Boston"), please take a moment to send me your new entry. I'll try really hard not to mess it up again! That URL again: http://www.cs.unc.edu/~yakowenk/classiccmp/ccrs_list.html Operators are standing by. :-) Thanks, Bill.

25 years, 9 months

Microsoft is about to arrest me!

by lundo＠interport.net

Oh, god! Does Lord Gates now even have his own police force?? I think their arrest powers would have to be severely limited - though you might have a long Supreme Court battle ahead of you to get out of MS Jail. -- +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + Robert Lund | "So many good ones, and so many bad ones; + + lundo(a)interport.net | that's what you get for trying." + + New York City | Dutch Schultz, last words + +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

25 years, 9 months

Fooling with floppy drives

by edick＠idcomm.com

There are also the "digital" alignment diskettes. These have certain forms of misalignment intentionally written to certain tracks in a certain way. Together with appropriate software, you can ostensibly detect, quantify, and correct (if you know how and feel you can do it) whatever defects it finds. I've read about this but never got around to trying it. I don't know anyone who's tried it, so I can't even ask the relevant questions. Dysan made a whole series of such digital diagnostic diskettes, as they were called, for various types of disk drives. Unfortunately, they were priced such that it was cheaper to buy a new drive than to buy one of these and the software and fix it yourself. IIRC the price would have crossed over at about 50 drives, not counting the labor savings, since I provided that. The analog alignment process is quite straightforward, but not something I want to do again. Moving the heads back and forth, then tightening the screw holding the lead screw/motor in a fixed position only to have to repeat the process because the changing stresses from tightening things down has caused them to move . . . UGH! . . . Dick -----Original Message----- From: Dwight Elvey <elvey(a)hal.com> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Thursday, April 08, 1999 4:53 PM Subject: RE[2]: Fooling with floppy drives >Steve Robertson <steverob(a)hotoffice.com> wrote: >> >> 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? > >Hi > I've used alignment disks. You need an oscilloscope >to use them. You also need to write a low level >driver to keep the system from freaking when doing >the actual alignment check. They record two signals >on the disk that are 1/2 track above and below the >normal track position ( I don't recall what track you >select but as I recall, it is about half way up >the disk ). The two signals are exactly 1 cycle >per revolution of the disk different in frequency. >You look on your oscilloscope at the analog signal >that comes out of the read amplifier and adjust >for what is call a cats-eye pattern. If the track >alignment is right on, you'll have equal height >signals from the first half of the revolution >as the second half ( sync of the index pulse ). > They also include a constant amplitude track. This >is used to look for contact problems of the disk/head. >One another track they usually have several different >frequency tones recorded. These are used to check the >band pass of the drive. > Other than the cats-eye pattern, there is usually little >that you can adjust on a finished drive. The cats-eye >pattern can be used to fine tune the stepper position. >There are usually some slotted screws someplace that allow >slight changes in the rotation of the stepper. One does >have to check the proper operation of the track zero >sensor after this adjustment because there is interaction. > As for price??? I bought the one I have at a surplus >shop for $1. >Dwight >

25 years, 9 months

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test-drb April 1999