Archive for the ‘Apple 1’ Category

fixed 6502/Apple 1 Cheat Sheet

Friday, February 6th, 2015

Apple 1 6502, cheat sheet, v.98

I fixed the definition of the ROL and ROR instructions.

6502 memory test gotcha – 6502 cheat sheet error

Friday, February 6th, 2015

One of the more popular programs that I’ve written is this 6502 memory test. One person using this test to checkout his Mimeo, recently discovered that it doesn’t work with his early white 6502. Turns out that that particular 6502 is a nice collectors piece, without a functioning ROR instruction. I used the ROR instruction at the end of the third test, so the program hangs when run on an early 6502 with the missing ROR functionality.

; all test 2 passes complete – prepase for test 3
LDA #$7F
BNE NX_TEST ;always branch

CHK_TEST3 ;floating zeros in progress or done
CPY #3
; pass of test 3 complete – 8 passes in all with 0 in each bit position
ROR TEST_PATRN ; rotate right – Carry to MSB, LSB to Carry
BCS NX_PASS2 ; keep going until zero bit reaches carry

I haven’t checked it, but I think the following code will accomplish the same basic test without using the ROR instruction.

; all test 2 passes complete – prepase for test 3
BNE NX_TEST ;always branch

CHK_TEST3 ;floating zeros in progress or done
CPY #3
; pass of test 3 complete – 8 passes in all with 0 in each bit position
ROL TEST_PATRN ; rotate left – MSB TO Carry, LSB = Carry
BCS NX_PASS2 ; keep going until zero bit reaches carry

I recently discovered that my 6502 cheat sheet has an egregious error. The ROL and ROR instructions move the Carry bit into the LSB and MSB (respectively), not the MSB and LSB. In other words the instructions are rotate through carry instructions.

I’m not sure how I managed to mess this one up or why it took so long for me to notice this or why no one else noticed it. Perhaps the functionality of these instructions are so well known that most people don’t need to refer to a cheat sheet to understand functionality. Clearly, I knew how they worked (or were supposed to work in the case of the early chips) when I wrote the 6502 memory test.

Brain Boards Sold Out – summary of pending projects

Friday, January 9th, 2015

I built and tested the last two kits over the holiday break and sold them on eBay. I made 59 PCBs, and kept 1 for myself, so there are 58 that were sold, either as kits or fully assembled.

Once the initial interest passed, they were very slow sellers, so I’m not expecting to make any more. I have some ideas for an enhanced version, but that is very far down my list of things to do, so I don’t know if or when I’ll take the time to work on that.

Here are just a few projects on my backlog that are ahead of the enhanced Brain Board. These will easily keep me busy for a couple of years or more.

  • Finishing all the SCELBI I/O Boards
  • Getting Apple II RTTY on the air – reception is working – transmission software is coded, but needs lab testing prior to actual “on air” tests
  • Getting vintage computer Morse code encoder/decoder on the air – Jack Rubin sent me an early Byte Magazine article with a 8008 software package for this, so I’ll probably do this on the SCELBI
  • Fabricating SCELBI Chassis Components
  • Putting together the VCF East 10 display and “Fix It” lecture
  • Hack together a Mimeo with 20K DRAM
  • Move Apple II RTTY application to the Mimeo/Apple 1
  • I have identified another board that is rare, of historical significance and worthy of replication
  • I have other ideas, that are even further out, such as doing a Mark-8. If I did a Mark-8, I would probably etch my own boards. This would probably be pretty easy to do, as the artwork was published and there was no solder mask and the holes were not plated through. I don’t think I would make batches of boards for sale, as this has been done already, and some of the parts are in the harder to find category.

    I also really need to do a manual/book on the SCELBI and I have made some half hearted attempts to start this. The main obstacle is that I’d want to scan and OCR the original docs and that is a very laborious process.

    Brain Board Inventory Down to Two Kits

    Thursday, December 4th, 2014

    I have two Brain Board Kits left and don’t think I’ll do a rerun anytime in the near future.

    I had a total of 59 made in early 2011 and it’s taken a while to sell the last few kits after a fair level of initial interest. Given the numbers made, these are likely to be hard to come by in the future. If you don’t already have one, this may be your last opportunity to get one for some time.

    Bob Bishop’s Apple 1 Trade In Deal – and just when did Apple II’s first ship

    Monday, November 17th, 2014

    Apple 1 and Apple II programmer, Bob Bishop recently passed away. Though I didn’t know Bob Bishop, I did exchange a few emails with him in June of 2013. From the few emails I exchanged with him, I got the impression that Bob was a good guy, and I feel it’s unfortunate that I never got to meet him in person.

    Back in June of 2013, while refining the Apple 1 Registry, I noticed that at one time, that Bob had an Apple 1. I sent him an email, asking if he still had his unit. Bob replied, saying that he had traded it in. This was about the time that Fred Hatfield’s Apple 1 was sold at auction. There was much in the press about Fred’s Apple 1, which included a letter from Jobs, offering a trade in deal. This was a deal which Fred had refused. Bob was a little concerned that the trade he made, wasn’t as good as what Fred and others were offered.

    Here is the story of that trade in, in Bob’s words. The article he mentions, was a New York Times article that included some mention about how aggressively Apple pursued the Apple 1 trade in program.

    When I read that article, I was a little upset (and said so on my weekly radio show) to discover that the company had “an aggressive trade-in program, offering Apple II’s and sometimes cash incentives in exchange for Apple-1’s.” When I wanted to do MY trade-in, I had to go to apple and ask THEM if they would be willing to do it. They said YES… but only if I paid THEM some additional money! But I guess that was before they had fully started their trade-in program. So it may be that I have the dubious distinction of having been the very first person to trade-in my Apple-I for an Apple-II (since the serial no. of the Apple-II that I got was 0013). :)

    But now that you’ve showed me the original letter from Fred, It looks like the NY Times article may have gotten their information a little mixed up. According to the letter, it appears that Fred had to pay THEM the $400 — and not the other way around (just as in my case).

    I don’t remember exactly how much I had to pay when I made my trade-in, but I think it was about the same amount ($400). And I made the trade-in around late June of 1977, but Apple didn’t ship the computer to me until July. (I remember that they said it would be delivered to my home in the next few days. So on July third, I sat around anxiously waiting for delivey. The next day was going to be the Fourth of July, and if it didn’t come today, I would have to wait two more days to get it! Well, it didn’t come… so I had a very miserable Fourth of July that year. But around 10AM on July fifth, it finally arrived! :)

    – Bob -

    By the way, surviving evidence indicates that though Apple 1 trade ins occurred, it wasn’t a real great deal. Several surviving Apple 1’s that came through the hands of early Apple employees, were probably trade-in’s, but there aren’t that many of them. The only person that I know of, that actually acknowledged that he traded in an Apple 1, was Bob Bishop.

    Woz’s take on the Apple 1’s noisy -5 volt supply

    Thursday, October 30th, 2014

    There was a recent thread about the Apple 1’s noisy -5 volt supply on Applefritter, so I asked Woz the following:

    One thing a number of us have noticed while working with reproductions of the Apple 1, is the amount of noise that exists on the -5 volt supply. The stabiliy of the -5 volt rail appears to be affected by the edges of the -12 volt clock that is used to control the video shift registers. Usually it’s not a problem, but I’ve run across a few cases where it affected DRAM reliability. Adding additional decoupling to -5 near the shift registers and the -5 regulator seems to clean things up considerably.

    I was wondering if any of you remember noticing that noise on the -5 volt supply and if that ever was an issue back “in the day”.

    I recieved the following reply from Woz:

    I am sure that what you describe is valid, although I personally wasn’t aware of it.

    I did the prototype of the Apple I and debugged the PC board version but didn’t look into such aspects. I’m sure you are quite correct. We knew that this was a low volume product since we were demonstrating the Apple II before shipping the first Apple I. Hence, we did not have many to become aware of issues like this. Part of the problem was that my time was being spent on the Apple II completion.

    The ‘productizing’ of the Apple I came under Steve Jobs. I always optimized my prototypes for short distance wiring, but the PC board introduced longer power traces. Please forgive me. I never looked closely at this aspect. I certainly over-minimized in bypassing decoupling capacitors throughout the chips and RAM. I did worse too that was probably copied over to the PC board, like not having pullup resistors on unused TTL inputs. Still, had we at Apple been aware of such an issue while selling maybe 150 Apple I’s, we could and would easily and quickly have rectified it. But we didn’t test fully a product that was a temporary place-holder before the big product. We did try to buy back every Apple I in exchange for Apple II’s.

    We had more luck than anyone deserves with things working out just enough to suffice and do what we did.

    I will tell you that I and others did observe the power lines and did not notice noise or spiking. And, as I said, it was never a problem that was called to our attention, or at least to my attention. We could have put out an errata sheet for owners to fix the problem themselves, since this was very much a maker product (local stores could modify things to use 16K RAM’s, for example, and they did.

    I am totally interested in hearing such things even after all these decades. I awoke one night in Quito, Ecuador, this year and came up with a way to save a chip or two from the Apple II, and a trivial way to have the 2 grays of the Apple II be different (light gray and dark gray) but it’s 38 years too late. It did give me a good smile, since I know how hard it is to improve on that design.


    Apple 1 Registry highlighted in Robb Report Collection

    Tuesday, October 7th, 2014

    I was mentioned in a Robb Report article about the collectible value of vintage computers. It’s always an honor to be mentioned in the same article as Dag Spicer of the Computer History Museum.

    Apple 1 Registy updated and new SCELBI registry

    Sunday, September 14th, 2014

    I just posted an update to the Apple 1 registry. One system was deleted and one added, so the total count holds at 63. The new one is John Anderson’s, which will be sold at auction, next month. I just was contacted by the owner of what is probably an unlisted system, so the count could grow to 64, very soon. Christopher’s system, which has been shown at K’Fest, VCF midwest and VCF east has been undergoing some restoration, so I added an updated image and additional information.

    Note that the success of the Apple 1 registry is largely due to contributions of owners and former owners and other interested parties and I greatly appreciate all new information.

    What’s really exiting to me is the new SCELBI registry. If you think Apple 1’s are rare, I could only find information on 13 SCELBIs. I recently received information on what could be a 14th, but it also possibly could be the missing Freeman Museum unit. The images on the SCELBI registry will be a little different than the Apple 1 registry, as the images will emphasize the quirks and differences between the units. Many original SCELBIs don’t exactly look like factory stock systems, so Iit should be a good resource for people building reproductions.

    I expect that some of the information may be incorrect. Bear with me as I expect to refine this registry quite a bit in the future.

    Dover Mini-Maker Faire Experience

    Monday, August 25th, 2014

    Dover, NH Mini Maker Faire

    Dover, NH Mini Maker Faire

    Just sharing some experience from the Dover Mini Maker Faire which was Saturday. I had Micro – Chess going on the Mimeo and Dave Ahl’s HI-LO in tiny SCELBAL (integer BASIC) on the SCELBI. It was busy almost the whole day, just a few fairly brief periods between visitors. It seemed a bit busier than Saturday at VCF.

    HI-LO was the perfect text game for casual visitors of all ages – simple to teach and quick and easy to play – I was impressed by the number of small kids that immediately proceeded to use a binary search algorythm to find the number.

    A lot of people tried a few moves on chess, but the user interface is so awful on the Apple 1 port of micro-chess – I had to train almost everyone – even though I had instructions posted.

    I met an original Mark-8 owner(still has his system). That guy added a digital group video card to his Mark-8 and made some improvements to it, which were used by later generation Digital Group video cards. Another person who was into SWTPCs in the day. Another person that was once vice president of the Boston Computer Society. And finally, another guy who worked with Draper Labs on the Apollo guidance system computer.

    There was a wide variety of exhibits from art and crafts to a young man who was building a neutron generator. If you have a mini-maker faire in your area, I’d say it would be worthwhile to show off your gear – you might meet some interesting people.

    Briefcase Apple 1 Sighting

    Wednesday, August 13th, 2014

    There are a couple of original Apple 1’s that were put in briefcases.

    One is owned by the “Main Personal Comptuer Museum” and is depicted on my registry page.

    The one of interest for purposes of this blog entry is shown in an image shown on a webpage put up by the Silicium Museum organization. I don’t believe that the briefcase unit is the actual Apple 1 owned by the silicium organization. In fact, since I don’t have good documented images of their unit, I am just a bit skeptical about whether Silicium actually has an Apple 1. My standards for posting original Apple 1 information has risen since I added the Silicium unit, and if I recieved a similar report today, I might not have added their unit to the registry, at least until I recieved a good image.

    However, it is interesting that I just got another historic look at this same briefcase Apple 1. It was shown on the program Computer Chronicles, which has it’s shows archived at the site It can be seen at the beginning of a show entitled“Apple II Forever”.

    I may have to add this unit to the registry, as a missing historic unit. There is a reference in the show to it being a museum piece. Since the show might have been taped in California, maybe it’s still sitting in some museum vault in the Bay Area.

    By the way, there is no better way to understand the history of personal computers than to read vintage publications and view vintage videos. The archive of “Computer Chronicles” show is priceless. Check out Bill Gates participating in the Computer Bowl II.