Archive for the ‘Vintage Computing’ Category

Proposed PS/2 Keyboard Adapter Stretched Strobe Change

Friday, April 11th, 2014

As I mentioned in a previous post, my PS/2 keyboard adapter requires some strobe stretching in order to work with some kinds of early microcomputers, such as some OSI models.

I think I have come up with a convent way to accomplish this, with only a small firmware change.

Here is what I have in mind.

As before, when the CR jumper is inserted, it disables recognition of the CNTRL-RST and CNTRL-CLR keyboard/RS232 sequences, which assert the reset or clear screen outputs, as appropriate. With my new design, in addition to disabling the aformentioned reset and clear sequences, inserting the jumper will change the clear screen output to an input. Now here is the key part of the change; whenever a character is typed and strobe is asserted (high true), if the CR jumper is inserted, strobe will remain asserted until:

  • minimum of 125 useconds have elapsed AND
  • the input to the clear I/O port is asserted (also high true)
  • To maintain current behavior (a 125uSec long pulse), you just need to tie the strobe output directly to the clear input.

    In order to stretch strobe out a bit, you have a few options:

  • Tie strobe output to clear input through an RC timing network in order to slow down the response to the clear input. For example – connect strobe and clear together with a 10K resistor. Then connect the clear input side of the resistor to a 1 uF capacitor and connect ground to the other side of the capacitor. Doing a basic RC timing equation shows that this should yield a delay of approximately 10 milliseconds. Change the values to attain a strobe length that meets your requirements. You do have to be careful to limit current through the resistor, so you don’t blow the strobe transmitter, though.
  • Use external logic of your choice to assert the clear signal to the PS/2 adapter
  • Behavior with the CR jumper disconnected is exactly the same as with the previous version of firmware.

    The main assumption behind this change is that the clear output, is only required for the Apple 1. I have found little to no need to disable CNTRL-RST and CNTRL-CLR on the Apple 1 (or Apple II) and those features are probably of little value to other platforms. In any case, the PS/2 keyboard sequence of CNTRL-ALT-DEL will still assert reset no matter whether the CR jumper is in place or not. In fact, using the CNTRL-ALT-DEL combination from a PS/2 keyboard will be the only way to assert reset if a system needs both reset AND a stretched strobe output. Said another way, you will not be able to assert reset from a device connected with the RS232 port, if your system also needs a stretched strobe.

    I’ll do some trials over the weekend and assuming that it works ok and I get no better input or ideas, I’ll have a new version of the firmware available very soon, possibly as soon as next week.

    SwyftCards Now Generally Available

    Friday, April 11th, 2014

    Swyftcard kits are now generally available for $55, which includes shipping.

    Check out my SwyftCard page for more information about the SwyftCard and Information Appliance, Inc.

    Or send email for ordering information.

    PS/2 keyboard adapter used with Ohio Scientific Computers at VCF

    Thursday, April 10th, 2014

    It took a modification, but Bill Dromgoole was using my PS/2 to parallel keyboard adapter in his display of OSI computers at VCF east 9.1. (The link to the image of Bill’s setup from the Vintage Volts blog). The modification was to stretch the strobe output with a 74123 one shot IC.

    PS/2 to parallel keyboard adapter

    I didn’t anticipate this when I made the design, but some vintage computers poll the strobe directly with software routines, while waiting for new input. My design assumed that strobe would be used to latch a flip flop (or equivalent), which would be reset by software when it actually read the character. I’m not sure how long Bill stretched the strobe, but with an 74123, it’s easy to adjust the pulse. Another person, told me at VCF that did the same thing to make the adapter to work with his vintage system. Unfortunately, I can’t remember who the second person was.

    At some point, I’ll probably look into stretching the pulse in firmware, or at least adding a configuration option to stretch the pulse.

    Problems with 8008 serial routines that posted

    Saturday, March 22nd, 2014

    Just a heads up – the serial transmit routines that I have posted with the 8008 applications have serious issues. Though it was working for me, other were using serial ports that weren’t so forgiving and had problems with transmit. Finally Corey Cohen tracked down problems with start and stops bits used with the transmited data. As soon as I get a chance to check out the fixed routines, I’ll be updating all the applications on my 8008 application and BASIC pages. For those of you that can’t wait here is the code for a version that I think will probably work. This version is timed for 2400 baud.

    My OS/X emulator was also broken and needs an update, as well.


    NDI 177 ; mask MSbit
    CAL BITOUT ; 1
    CAL BITOUT ; 2
    CAL BITOUT ; 3
    CAL BITOUT ; 4
    CAL BITOUT ; 5
    CAL BITOUT ; 6
    LDA ; timing delay
    LAI 200
    OUT OUTPORT ; stop bit
    LDI 100 ; and extra for inter character spacing

    RRC ; shift to get next bit
    LDI 3
    LAA ; nop to delay 5 states to make timing work
    LDI 0 ; delay 8 states

    Reproduction SWYFT CARDs Arrived

    Friday, March 14th, 2014

    I just got my reproduction SWYFT CARDs in and they look and work great.

    Reproduction SWYFT CARD

    Reproduction SWYFT CARD

    I’ll be releasing them at VCF east in a few weeks. I’ll also be doing a soldering workshop in which you will be able to build one, even if you are a novice at soldering.

    Reproduction and Original SWYFT CARDs

    Reproduction and Original SWYFT CARDs

    The SWYFT CARD was used as a prototype/proof of principal implementation by Jeff Raskin’s company, after he left Apple after the falling out with Steve Jobs. Later they came out with the SWYFT Computer and the Canon Cat.

    Check out the VCF website for details on VCF east 9.1

    Mike W.

    Mimeo’s back in stock

    Monday, February 24th, 2014

    Will be picking up the latest batch of Mimeos from the PCB fabricator this week (probably tomorrow). No changes from last batch.

    At this point, I think I have some stock of all the PCBs that I have made since I started on this retro computer hobby.

    Send an email if you have any questions or interest.

    Kit and PCB status update and a question

    Saturday, February 1st, 2014
  • Coming for VCF east – SWYFT card reproduction kits – special introductory price if you join my SWYFT Card soldering Workshop – $40, drop me an email to register. Part of the proceeds goes to help support MARCH. After VCF east, price goes to $50.
  • Mimeo’s – out of stock – expect to have new batch around end of February
  • Datanetics PCBs – 1 left – rerun timing TBD
  • Brain Boards – 9 left – Note that I’m going to try move the remaining Brain Board kits over the next few months. I might even list them on ebay, to clear them out. If you want one, time to get it, is now. A rerun is not likely to be in the “cards”. I have a vague idea for an enhanced firmware board that may or may not get traction someday in the future.
  • SUPERPROTO kits – 8 left – rerun TBD – these are slow sellers and I haven’t actually made any money on these. However, I find them useful for my own purposes, so I might do another run (someday).
  • ACI kits – plentiful (currently I’m running low on PROMs, but expect I’ll be able to find another batch without too much trouble)
  • PS/2 keyboard adapter kits – plentiful
  • A2 rev 0 – ample supply
  • SCELBI 8H – I have less than 10 8H board sets remaining. I’ll make extra SRAM PCBs, when needed. Front Panels are in limited supply (less than 15, I think). TTY boards are plentiful
  • Now for the question – should I call my Apple II rev 0 reproductions Mimeo IIs, even though they came first?

    reproduction SWYFT cards for the Apple IIe coming

    Sunday, January 26th, 2014

    I plan on holding build your own SWYFT card workshop at VCF east in April

    follow the sessions link to find information.

    If you don’t know what a SWYFT card is. Check out this link.

    Mike Willegal

    Apple II Hedlock Fastener Repair

    Saturday, January 18th, 2014

    The “Hedlock” connector on an Apple II is the fastener that holds the lid of the case to the case. It is similar to a 3M Dual Lock reclosable fastener. On the Apple II, it is attached to the enclosure and lid with double sided tape. Over time, the adhesive loses it’s effectiveness and the Hedlock connector comes loose from either the lid or the base of the computer’s enclosure.

    Here is an example where the tape stayed with lid, but the fastener came loose.

    Delaminated Hedlock Fastener

    Delaminated Hedlock Fastener

    I used to use contact cement to reattach the fastener to the tape, but I found over time that the contact cement is less than an ideal solution. I think I found a better solution using the tape found in auto part stores that is intended to reattach loose trim pieces. This 1/2″ wide double sided tape has an extremely strong, long lasting adhesive on both sides, so I expect this solution to be an improvement over the contact cement approach.


    Before attaching this new tape, you should remove the old tape and adhesive. This is, by far, the most difficult part of this job.

    In this example the old tape, which was attached to the lid, simply pealed off.

    Old Tape Removed From Top

    Old Tape Removed From Top

    The adhesive remaining on the Hedlock fastener was another matter. The bond is very strong, and in this case I eventually resorted to using a X-acto knife with a chisel blade to remove it. I left a few nicks in the surface, but since this is covered up with the new tape, I figured it wasn’t the end of the world. In a previous case, I managed to do it by rubbing with my thumb, but I ended up with a large blister on my thumb. I was temped to try a solvent like Goo Gone, but didn’t want to risk damaging the fastener. Here is the back of the fastener with the adhesive removed.

    Old Glue Removed From Hedlock Fastener

    Old Glue Removed From Hedlock Fastener

    Before reattaching the fastener, I cleaned up this area of the lid with Isopropyl Alcohol.

    Next I pealed back a strip of the new tape and stuck it to the fastener and cut the tape off from the roll.

    New Tape Applied to Hedlock Fastener

    New Tape Applied to Hedlock Fastener

    Then I took a sharp scissors and trimmed the ends of the tape to match the curve of the ends of the fastener.

    New Tape Applied to Fastener and Trimmed

    New Tape Applied to Fastener and Trimmed

    The last steps are to remove protective backing from the adhesive tape and carefully press the fastener back in place.

    Hedlock Replaced

    Hedlock Replaced

    I don’t know if it makes a difference, but I would wait a day before putting any stress on the reattached fastener.

    Reproduction Apple II rev 0 update

    Friday, January 17th, 2014

    Here is an image of my completed prototype.

    2014 edition A2 rev 0

    2014 edition A2 rev 0

    The image can also be found on my website.

    This has taken much longer than expected, but I’ve got a few good decal sets ready and will start taking money, with shipments beginning no later than 1/27, with the first units likely to ship on 1/20.

    The build manual can be found here.

    Parts list can be found here.

    Cost of bare PCB is $150 plus $20 shipping. In order to make a functional board, you will need to provide components, keyboard (my PS/2 keyboard adapter works with Apple IIs), power supply (from Apple II plus), and ROMS (see my ROM page). I’ve heard from Rob at Unicorn and he might be putting together component kits (no ROMs).

    If you are not into building kits, but you are a Apple II fan, keep in mind that a framed bare PCB would look great in your den.

    Send an email if you need more details about ordering.