Indus GT CP/M Experiments

Entry posted by Stephen October 12, 2011

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After much trouble, I now have a few working CP/M disks. I will detail the process of getting images from the internet to a working CP/M floppy in the coming days. For now, I will show how I changed the god-awful colours of the stock Term-80 program.

Here you see the before image. I am running MS BASIC-80 Ver 5.21 on top of CP/M 2.22. This is running on a 64kB Z-80 system (the controller of my Indus GT disk drive)

Knowing that the Atari's color registers start at $02C0, I fired up the Term-80 program in Atari Win+ and inspected the word of memory starting at $02C0

I then used my trusty 130XE, MyDOS 4.53, and APE 3.06 to transfer the Term-80 executable to my PC. I loaded it into Notepad++ and jumped to the hex editor. The first four bytes tell me that it is a binary file which loads at $6000.

Here's the cheat-sheet I made, describing the three colour registers I need to change, and the offset into the code (taking the 6-byte header into account).

Knowing the start address of the program, I disassemble RAM starting at $6000. Scrolling down a few pages, I reach offset $AE and see the LDA/STA pair that sets the cursor colour (PCOLR0). This means I need to change the byte at offset $B4 in the hex-editor.