Commander X16

I see, it was because of how ADDR0's half-increment was implemented. If ADDR0_INCREMENT is 0.5, and ADDR0_NYBBLE is LEFT (0), then ADDR0_CHANGE is 0. If ADDR0_INCREMENT is 0.5, and ADDR0_NYBBLE is RIGHT (1), then ADDR0_CHANGE is +1 byte. If ADDR0_INCREMENT is -0.5, and ADDR0_NYBBLE is LEFT (0), then...

I'm looking at the pull request just out of curiosity. What was the issue? When the "sometimes" increment was horizontal, it advanced a byte instead of one nybble?

"S" means "scratch" (as in, scratch it out by squiggling a line through it), and the "0" means "Drive #0", which is a leftover from the two-disk-drives-in-one-device PET days. Look up the 1541 or the 1571 user guide if you want to see it in context. I don't kn...

Welcome! Glad to have you here. :D Another thing I wonder is how to get a look at the VERA source code, because something I'd like to see in the line draw helper is a way to have the function invert or increment the color of pixels as it draws. The VERA source code is in Verilog can be found in this...

Actually after a nudge on the discord, I tried making a SPRITE based version as well. I didn't fully finish it but it actually was simpler to write than this tile based one. I was drafting up a game idea, and being able to use a sprite as a bitmap canvas seems like it'd be really powerful. I was go...

SAVE has a couple of shortcomings. One of them is the inability to save from VRAM, but another is the inability to save from banked RAM. That is, when you LOAD to banked RAM, it automatically handles wrapping from $BFFF to $A000 and increasing the RAM bank. SAVE doesn't have any knowledge of banked ...

I don't know about the rest of the memory. But somewhere around r45 they did start initializing the Palette Ram on boot so those should be reliable. (512 bytes starting at 1:$FA00) I thought so too, I double checked, and it does, so that's not the issue. The problem seems to be simpler: the monitor...

Asking on Discord can yield faster responses, but if those questions and answers don't make their way back here, then nobody else will benefit from the knowledge. It's kinda like if I ask a question and someone replies with "I sent a PM", and then that's the end of the discussion. It helpe...

When you READ from VERA 1:F9C0..1:FFFF, you don't get the contents of the register, but rather the last byte written to that address by the CPU . On a cold boot, those values are unpredictable even if the registers themselves are initialized. This information comes from here , the VERA chapter of th...

(As a side note: I'm not proposing a 1:1 re-print. I'm not sure who holds Commodore's old Copyrights, or if anyone can reasonably claim them. I think that, instead, I'd simply start with the VIC-20 guide's outline and write the chapters from scratch, covering the same basic points. ) Oops, I wasn't...