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Thread: Adding lowercase to a Model 1 in 2016

  1. #1

    Default Adding lowercase to a Model 1 in 2016

    Perusing forums and images, I sometimes feel as though I have the only Model 1 that was never treated to the lowercase conversion. While I have lived with uppercase only, the addition of much "new" software to my library (thanks Pete) has made me realize the limitations every time nonsensical characters take the place of what should be elegantly displayed lowercase type.

    In researching the various methods out there, it was noted that a conversion to lowercase was not itself without problems and that some software actually did not support it at the time. In fact, a physical switch was included to go back to uppercase only for those instances.

    Fast forward 30+years, and I am wondering if those "uppercase only" titles were eventually made compatible with lowercase (ie, LDOS would recognize it and install the driver), and if enough of them exist to warrant a hardware switch to revert back.

    Unless someone can suggest a better alternative, I think I am most interested in the one given on Ira's page: (4th down from the top under Model I)

    http://www.trs-80.com/trs80-zaps-hardware.htm


    Questions for those in the know:

    1/ As discussed above, is the toggle switch necessary to include? Are there any "must have" software titles that are uppercase only?
    2/ With regard to the 2102 and 7486 ICs, I have noticed several derivatives. Is there a particular part ID to look out for?
    3/ As I understand it, a proper conversion would include a new character generator that would properly display lowercase descenders. I am guessing that may be impossible to come by these days? Is that a big deal and something that can be included later if I come across one.
    4/ Is there a better alternative for the conversion than the one given above?

    Any other guidance, tips and suggestions would be appreciated!

    Cary

  2. #2

    Default

    I got by during the original useful life of my Model I using the very simplest lowercase mod with no toggle switch. It didn't have lowercase descenders, but it was a heck of a lot better than uppercase-only. I don't recall any software being incompatible with it. I got the design from some magazine of the time and implemented it myself while in high school. It went something like this:

    Piggyback the 2102 SRAM chip onto Z45 (except pins 11 and 12--bend those two to stick out horizontally and trim off the thinnest part). Wire pin 11 to Z60 pin 5. Use OR gate Z73 pins 11, 12 and 13 (I don't recall if I had to cut some PCB traces to free up the unused gate). Wire Z73 pin 13 to the 2102 pin 12. Cut the trace on Z30 pin 13. Wire Z30 pin 13 to Z73 pin 12. Wire Z73 pin 11 to the trace formerly driven by Z30 pin 13... Z60 pin 4 or Z27 pin 13.

    Pretty simple and only the one new chip.

    The 2102 SRAM chips are pretty ubiquitous... here's a cheap one:

    http://www.electronicsurplus.com/nat...-sram-1024-bit

    The "L" variants like the originals are just low-power versions, with even lower power consumption in "standby" mode--which the TRS-80 screen RAMs never do.

    As far as the 7486 (if you decide to use that mod) what you want is SN74LS86.

    Pete.

  3. #3
    Join Date
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    Default

    I used the "Electric Pencil Mod" and installed the switch. I hardly ever used it. I did have the newer character generator ROM, which will be difficult to impossible to get now.

    Maybe someday, someone will make an adapter to use a burned EPROM.
    -----[ Al ]-----

    3 - TRS-80 Model I, TRS-80 Model 4D, LNW-80 Model I, Coco, 3 - Coco 2, Coco 3, 2 - Tano Dragon 64, C64, C64c, C128, 2 - Atari 800XL,
    Atari 520-ST, Atari Mega-2 ST, Amiga 1000, TS-1000, TS-2068, ZX-Spectrum, IBM 5150, 2 - Apple ][gs, Laser 128, and a butt load of Macs and Intel PCs.

  4. #4
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    Mine has the official Tandy mod with newer character generator ROM. No switch needed. 2 wires and a trace cut. That is all.

    Look at your character generator and id it has part number 6671 no descenders. If it has a 6673 it will have the descenders.

    @avia that mod is overly complicated.

    Looking at the 2 pictures: Pic 1 shows two wires attached to the piggyback RAM chip. Red wire goes to Pin 13 of Z27. Green wire to pad coming off Z44 pin 13.
    Pic 2 shows Z29 the character generator ROM and overall the whole mod.

    To the right of Z29 is the trace cut very easy to see. It is the thinner of the 3 traces to the left of Z30.

    And that is it. Simple.
    Attached Images Attached Images
    Last edited by Chromedome45; July 6th, 2016 at 12:36 PM.
    *FrankG*

  5. #5

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    Yeah, you don't need the inserted spare OR gate if you have the newer character generator ROM, but if you do you probably already have the lowercase mod.

    The OR gate (Z73 pins 11/12/13 or one of the unused gates on Z23--as I recall these were harder to "free up" for use) is needed because the older ROMs have the funny widget characters as codes 0-31, whereas the newer ROM had a repeat of the uppercase letters. Z30 pin 13 needs to be ORed in with the new SRAM bit to prevent showing the widgets instead of uppercase characters in some older Level II ROM versions.

  6. #6

    Default

    There's a way to tell whether you have the old or new character generator ROM without opening the case: some of the non-lowercase characters are different between the two versions, at least if 80 US magazine July/August 1981 page 56 is accurate. For example, in the newer ROMs, the cursor character appears slightly below the uppercase letters. Also most of the characters are shifted upward by one pixel, making the tops of uppercase letters aligned with the top of a graphic block instead of one pixel lower. The dollar sign looks somewhat strange in the newer version.

    Did they really replace the grave accent and the tilde with pounds and yen? (You'd need the RS lowercase mod to see this).

  7. #7
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    Was just going by what was in my M1.
    *FrankG*

  8. #8
    Join Date
    Apr 2015
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    Morisset, NSW Australia
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    Quote Originally Posted by Avia View Post
    Perusing forums and images, I sometimes feel as though I have the only Model 1 that was never treated to the lowercase conversion.
    Just so you don't feel totally alone, my Model 1 is also UC only. FWIW I intend to keep it that way (for a "compare and contrast" with my M4). Though I do have vague plans to get a second M1 at some point as a second "compare and contrast" - that one would have Lower Case, hopefully 80-grafix, ...

  9. #9

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    After looking at it more closely, I'm deeply suspicious of the LC mod linked on Ira's website (the one by "The Peripheral People".)

    As far as I can tell, this mod was intended for diskless Model Is. It rearranges the character set in a way that requires a very specific driver; I don't think it would work properly under the DOSes I'm familiar with.

  10. #10
    Join Date
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    Wish you luck PJ on getting a 2nd Model 1
    *FrankG*

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