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memory locations for char set and what chars are where on the screen

Posted: Wed Nov 01, 2017 2:31 am
by Gregg Evans
I have two clear plastic hemispheres and I want to make a spherical led matrix powered by my 1000 and perhaps use it instead of a monitor. (wont have quite the res) where in memory is the char. set saved and more importantly there must be a place in memory keeping track of what char. is to be displayed where. Does anyone know where to find that?

Re: memory locations for char set and what chars are where on the screen

Posted: Wed Nov 01, 2017 3:10 am
by Gregg Evans
It will most likely be powered by an Arduino but will use the 1000 for its content. It might also be cool to just show the ram blinking away in a sphere like its thinking.

Re: memory locations for char set and what chars are where on the screen

Posted: Wed Nov 01, 2017 7:40 am
by mrtinb
The character set is stored at $1E00 - $1FFF.

The screen memory is a whole different story. It is the most complex of the ZX81/TS1000. Screen memory is floating around in memory dynamically after the program area. So if you add or delete a line in your program screen memory is moved up and down. On top of that each line is separated with $76 (newline). When memory gets tight the screen memory is collapsed removes spaces before $76 (newline). When this happens a black screen will be 25 $76 (newlines). The screen starts and ends with a $76 (newline).

More can be read here: http://problemkaputt.de/zxdocs.htm

Re: memory locations for char set and what chars are where on the screen

Posted: Wed Nov 01, 2017 7:45 am
by Paul
The characterset is at the very end of the ROM ending at 8191.
It contains 64 characters 8 byte each.
That gives you the beginning of the character set in ROM.
What is on screen is the content of the D-File (Display file)
It begins with a 118 and has 24 more 118, one for each line.
With at least 4K of RAM you have an expanded D-File which means after CLS you have 32 zeros between each 118.
With less than 4K RAM you will have a compressed D-File containing only 25 118s after a CLS.

Kind regards Paul

Re: memory locations for char set and what chars are where on the screen

Posted: Wed Nov 01, 2017 10:55 am
by Gregg Evans
Wow Paul that is exactly what I needed. I hope I can put it to good use. What a great group. Thanks.