Removing "official" TRS-80 Model 1 lowercase conversion kit?

Does anyone have instructions for removing the "official" TRS-80 Model 1 lowercase conversion kit? My Model 1 seems to have an issue with the kit, and for my purposes, it's completely irrelevant.

I've seen DIY instructions for other mods, but I'd like to see what the official mod. entailed, and how to revert it back to "normal".

Also, there was mention of a new character generator ROM for lowercase. Is the original ROM required to revert it back to normal, or will the new ROM essentially mimic the old one?



Thanks.

Old ROM or New shouldn't make a difference. If your ROM is an MCM6670 or 3108001 it is the old ROM. If it is an MCM6673 or 8046673 it's the new one.
As for info on the mod itself can't seem to locate it right now.

AN7000_Dude,
I modified my Model 1 so it had the Lower Case Modification. I also updated the ROM to a newer version. I've dug through my Technical manual, and I don't
have any detailed notes on what I did to install the lower case Modification. I'd have to open it up and have a look. It was documented in some article,
but it's been too long.

I even went to the basement looking for a lowercase kit, as I thought I had some still in boxes. But it was the Keypad mod for the Model 3. I had
remembered wrong.

I found an article from April 1980 Kilobaud Microcomputing p.132 & 133 about a Lowercase Modification.

In this article is the following basic program to test the LC Modification.

10 CLS
20 FOR A=0 TO 127
30 POKE 15360+A,A
40 NEXT
50 PRINT @ 640,""

You should see UPPERCASE, Punctuation, Numbers, UPPERCASE AGAIN, and finally lowercase.

I can scan the article and email it if you are interested.

After searching for a while, I found the April 1980 issue of Kilobaud Microcomputing with the article at:

[/quote]http colon slash slash archive.org/stream/kilobaudmagazine-1980-04/Kilobaud_Microcomputing_1980_April#page/n132/mode/1up[/quote]

http://archive.org/stream/kilobaudm..._Microcomputing_1980_April#page/n132/mode/1up

But, it isn't easily printed.

Larry

Custom TRS-80 book on p.107 says how to do the Radio Shack lowercase, just reverse the steps.

You don't even need to get rid of the extra video ram chip, just unsolder the two wires which go to it, restore the cut trace, and you are back to standard.

Level II Roms are compatible with any character generator installed, and if you have the Radio Shack lowercase then you WILL have 6673 installed. In unmodified state the 6673 works exactly the same as the 6670 or 001.

Ian.

Wish I had a 6673 ROM!

Thanks for all the replies!


Yes, it does have the 6673 ROM, and it's a "G" motherboard with the 2-chip Level II basic (but not the "R/S L2")

If it's simply the two wires and the trace-cut, I'll give that a try and see if it helps.


It's a very odd problem, since as I mentioned in the other thread, I can fill the screen with any(?) character and it's fine, or with graphic blocks. If it's not the lowercase mod, then it might be some weird glitch with the ROM routines that write the screen in the BASIC "editor" mode.

I'll try a few more test variations to see if I can come up with a consistent cause & effect.



Thanks again.

TRS-Ian said:

Custom TRS-80 book on p.107 says how to do the Radio Shack lowercase, just reverse the steps.

You don't even need to get rid of the extra video ram chip, just unsolder the two wires which go to it, restore the cut trace, and you are back to standard.

Level II Roms are compatible with any character generator installed, and if you have the Radio Shack lowercase then you WILL have 6673 installed. In unmodified state the 6673 works exactly the same as the 6670 or 001.

Ian.

Click to expand...

And this glitch is showing up just in Level II basic? Or are you using Disk basic? Assuming you have disk drives and an Interface.

The 2 ROMS are they in the normal ROM sockets? Not running by cable to a ROM board? Like the 3 ROM version?

OK, did some tests, and now it makes sense...

The Pound sign is CHR$(96), which is conveniently 64 above a space! If you had a bit 6 that is stuck, it will have no impact on graphics modes, right?


Now, is bit 6 the 2102 that is piggybacked for the lowercase mod?

I do believe so.

So it's possible your piggyback 2102 may be the culprit.

So I would say undo the mod. If your good at soldering I would say remove the 2 wires from pins 11 & 12 and the points they go to.

Find the cut trace and restore the connection probably the end points of 11 & 12. But not sure.

Now I would also carefully cut off the piggyback 2102 by snipping the pins close to the chip body and using a soldering iron to heat the connections and pull off the piggyback pins from the original 2102.

Make sense? Hopefully and good luck.

Done!

Works a treat... The piggybacked 2102 was the culprit, which seems a bit odd to me, but I don't fully understand how the bits are assigned with that arrangement.

Highly recommend this to anyone that sees Pund signs on their screen!

Yeah it's a strange layout. Why that was the 6th bit I don't understand. But I vaguely remember reading about it some where.

The original hardware of the Model I does some diabolical bit-shifting to get graphics and uppercase-only letters out of the 7 bits of video memory it has. If you look at an ASCII chart you'll see the characters that the Model I does have (basic punctuation, numbers, uppercase letters) occupy positions (decimal) 32 though 95 in the chart. Some binary math will show how this would cause a problem if bit six were simply "absent"; the original TRS-80 hardware used a few gates to magically generate a "fake" bit six as needed to paper over this problem.

The TRS-80 technical manual is pretty interesting reading. Radio Shack made some really... interesting choices, in a few areas to save a few pennies.

Read as cheap! But I have read some of it and it really is quite interesting what the Tandy engineers came up with. Very clever.