Recent content by gp2000

On Windows the preferences and settings are in the registry. They can be changed and deleted using regedit but one must be careful. Do the wrong thing in regedit and you can screw up your machine. The path is: Computer\HKEY_CURRENT_USER\SOFTWARE\Phillips\trs80gp Deleting the whole trs80gp...

In case it has any bearing on the analysis, the video wait states are suppressed when drawing the bottom 4 lines of a non-graphics character. Only the top 8 lines of a non-graphics character are pulled from the character generator ROM. The bottom 4 lines are always blank so there no need to...

Looks like the images in your post have gone away. I need to update my web page. The bug has been seen on other Model 3's but only early revisions of the machine. Tandy fixed it at some point. And the Model 4 circuitry is entirely different so I'm sure the bug does not apply there. I don't...

All Model 4's except the portable 4P have BASIC in ROM. If your Model 4 wasn't going into ROM BASIC when you hold down the BREAK key on boot there are only a few possibilities. You actually have a 4P (if the diskettes are oriented vertically it's a 4P). Or show us a picture. The BREAK key is...

As others have stated the PC-1 is a very closed system. We don't know the CPU instruction set. There is no known way to break out of BASIC into machine language. Extensive reverse engineering efforts will be needed to figure out the instruction set and see if there is any exploit to get...

Is the machine otherwise working? If you're getting some kind of MEMORY SIZE? or MEM SIZE? prompt (which would appear as MMR IE or MMSZ?) then it is the video circuitry. Otherwise the Z-80 isn't running and since it sets 64 wide mode the video could be OK. I'm not sure, but I think whether...

Reverse engineering is such fun. It is impressive to have caught on so quickly. I, too, have hacked Pac-Man: http://48k.ca/bacman.html Incidentally, MAME supports a cheat file format that will make modifications to ROM or RAM to give infinite live and such. Or just to make changes to a game...

Model II has a different character set; mostly like the original PC where the graphics characters are oriented towards drawing boxes and bar charts. But each character can be drawn inverted. As others have mentioned there's no POKE so you'll have to use "PRINT @" to display graphics. Here's a...

trs80gp comes with TRS-80 utility programs to import (and export) files to floppy disk. It's a little less convenient than external utilities like trstools or trsrwrite. For details see: http://48k.ca/trs80gp.html#impexp You'll also find some useful tips in Tim Halloran's video on...

By default zmac won't say anything unless there are errors. You could try zmac -h to display the help message as a smoke test. Seems likely your test run created several output files in the zout subdirectory.

That's a good explanation for why they took that approach. It also better explains how the Microsoft Editor Assembler for Model III line printer output works. Its "lprint" routine sends characters to both port $F8 and memory location $37E8. I fixed that by assuming that a real printer would...

That has to be a mistake; there's be no point in supporting those addresses unless they were writable. I took a look in the Model III Technical Reference manual and couldn't see where it says that. Do you have a page #? I'd like to note it as a correction.

That's correct. Matt Boytim was looking into this when doing some FPGA version of the TRS-80 and noted that the Model 1 aliased the 4 addresses while the Model 3 reduced that to two. I guess they figured it was enough for compatibility and didn't want to hide more ROM data than they needed.

Thanks! That's fantastic. It works in trs80gp. A quick scan shows at most 100 bytes difference in the various files on the diskette from TRSDOS 2.3. And all indications point to it being a patched version as opposed to having been re-assembled from source. Will have to do a deeper analysis...

The one with Japanese kana was the original version and is identical to the Model III. I don't know at what point they switched to the "international" version. The dividing line may be pretty fuzzy. Might be that most 4P's have the international. At a fresh start in BASIC you can see which...