C-128 80 column display and background color limits.

[Stephane Richard]

ok, right now, I can't seem to find the answer to this in any reference.  basically, when setting the background color of the 80 column screen i'm wondering if on a C129 (not an emulator) if I can use any of the 16 available colors or if I only have, say the first 8 available.

Reason for aslking, I seem to have problems doing that on WinVICE and before I report it as a bug, I wanna make sure it's not normal behavior and should be indeed reported.

Thanks all. :-)

[nikoniko]

Did you get this worked out? All 16 colors work just fine for me when selecting the background color in WinVICE. Some colors are similar to one another, though, so they may look like repeats because of that.

[Stephane Richard]

I think that's what the problem  is/was it could also mean I was looking at the 40 column colour layout chart at the time...lol...I need more coffee lol.

But I'll recheck and let you know shortly.

[Stephane Richard]

Well it seems you were right indeed nikoniko,

I did another test and yup, they do all work, and a few repeat themselves or are very close.  Now just be sure, if someone with a real 128 could test that on their 80 column monitor so we can put this subject to rest and/or I can report the bug to the winvice team. :-).

[nikoniko]

I made a screen capture of all the colors I get in 80 column mode under WinVICE 1.20, and produced a chart along with their associated RGB values. There are 16 distinct colors, though on my crummy laptop monitor black and dark grey look almost the same. This is in NTSC mode, by the way. I wonder if there's any significant different with PAL? I'll have to check that sometime.



I'm curious how close these are to how they'd appear on a real 128 with a Commodore monitor.

[adric22]

As I recall, the VDC could only use any of 8 background colors when in text mode.  I believe the reason for this was that the color register for each character was 8 bits.  4 bits for foreground and then 3 bits for background, and 1 bit for blinking.  I could be wrong, I'm not looking at any reference material.  But I used to do a lot of programming on the VDC and remember this.

[nikoniko]

Maybe there are some circumstances under which only 8 colors are available, but as far as the global color of the background I'm not aware of any limitations.

Attribute memory is arranged as:

Bit           Attribute
---      -------------------
7         Alt. Char Set
6         Reverse Video
5         Underline
4         Blink
3         Red
2         Green
1         Blue
0         Intensity

So you specify the foreground from any of 16 colors and the background comes from bits 0 to 3 of register 26.

Somewhere I think I've seen described a technique which tells the VDC to access text attributes the same way as graphic attributes, thus ignoring all the blinking/underlining/reverse video crap and allowing control over the background color of each cell. However, maybe I'm simply recalling someone's speculation.