Vintage Humor

I found this in Volume 1 – Issue IV of the SCELBI Computer Digest, which can be found online at scelbi.com.

THE NAVAL ADMIRAL HAD JUST PURCHASED A MINICOMPUTER TO HELP HIM RUN HIS MIGHTY FLEET. HE QUICKLY UNPACKED HIS UNIT, SET IT UP IN HIS STATE ROOM, PLUGGED IT IN, AND WITHOUT WASTING ANY TIME.. PROCEEDED TO ASK HIS NEW COUPUTER AN INPORTANT QUESTION.

“WILL THE WEATHER BE SUITABLE FOR LAUNCHING PLANES FROM MY AIRCRAFT CARRIER TOMORROW – OR WILL IT RAIN?”
“YES.” ANSWERED HIS NEW LITTLE BRAIN.
“YES WHAT?” SHOUTED THE EXASPERATED ADMIRAL.
“YES SIR!!” PIPED UP HIS LITTLE MINI.

skinned knuckles

Last night, a little after midnight, I finished replacing a power window regulator in my wive’s mini-van. I’ve done motors before, but not the regulator. I expected the job to come with a few obstacles to overcome and I wasn’t disappointed. I’d like to know how they connect the lock rods and lock actuator in manufacturing – what a pain. It also took some time and effort to get the window properly seated in the regulator guides, but I think that might have been an issue with the aftermarket regulator that I bought.

The reason why I do this is cost – my cost was $70. The last time I had one repaired by a shop, it was over $400.

Proposed PS/2 Keyboard Adapter Stretched Strobe Change

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.

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

    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.

    kb_adaptor
    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.