screen colors - machine language vs. pokes

[piranger]

I am trying to use the vicmon cartridge to write to $900F (36879) to change the screen colors.

when reading:
.M 900F
.:900F 1B 05 18 00 80

ok, that makes sense, as 0x1B =27 decimal, which p.36 of manual say is white screen with cyan border.

However, when I move my cursor over the '1B' and re-type '1B', the whole screen turns cyan (border and screen).

this is just one example. None of the colors match the table when using vicmon.

however, in BASIC, using pokes to 36879 and decimal values - no problem. it follows the manual.

what am I missing?

thanks

[piranger]

I did figure out that this works:

.A 1000 LDA #$1B
.A 1002 STA $900F
.G 1000


colors track the table

[joshuadenmark]

Hi Piranger

Welcome to our friendly forum, glad you figured it out

[piranger]

Thanks Joshua,

I guess there are registers the monitor just can only manipulate thru the accumulator.

Regardless, this cartridge is such a cool tool. Very intuitive to an assembly novice. I'm so
glad I jumped on it at the Classicgamefest in Austin last summer.

[Mike]

Hi, piranger,

[...] when I move my cursor over the '1B' and re-type '1B', the whole screen turns cyan (border and screen).

the extra bytes in the memory dump behind $900F contain invalid values that come from 'stray' read accesses to the VIA chips (address mirrors and tug-of-war between outputs are the keywords here).

I guess there are registers the monitor just can only manipulate thru the accumulator.

No worries, VICMON is perfectly capable of doing what you wanted. You just need to short the ".:" command on entry so only the byte to $900F is written.

You find more background info here: VICMON on VICE help.

Actually, I'd presume you also took the example from the techtinkering.com site. As stated by me in the other thread, it is a particularly bad example. It only works in emulation on very old VICE versions. These old versions were not accurate enough to emulate the address mirrors and tug-of-war mentioned above.

Greetings,

Michael

P.S. your machine code example needs to include a BRK instruction in $1005 to return to VICMON. It only worked by chance because the opcode value of BRK, $00, is very likely to be there. But it is not necessarily the case and then the CPU continues to execute whatever comes as code after the STA $900F instruction.

P.P.S. for more examples, there's always my primer thread for VICMON around.

[piranger]

hi Mike,

Thanks for the insights. Actually, I am working through the 'assembly with vicmon' tutorial (mary music player) where he shows directly changing memory values. I figured to try it with the screen colors too and hit the wall. Glad I didn't do the earlier tutorial first or I would have been xtra confused. I'll now keep emulator related bugs in mind if/when I run into another tutorial anomaly.

I still don't see how to change just 900F. I tried M 900F,900F but that still displays the whole line. I also tried typing over all 5 registers on the line and still get a full cyan screen. I'm missing the trick of showing just 1 memory value.

And thanks for the 'BRK' tip. I will remember and use.

Very grateful for the knowledgeable helpful community. I'll try to keep the dumb questions to a minimum and will definitely attempt to figure it out on my own first, but sometimes I strangely reach a solution only after using 'the confessional method' and posing the question.

Looking forward to walking thru your vicmon primer and making some "coloured birds" (after the obligatory modding of the mary code to play Alex's 'limelight' intro). Its funny you say 'Christmas morning' in your tutorial, as that is often where I project myself when sitting at the keyboard of this amazing little computer. Though if I had gotten it from santa 40yrs ago, I would wish also for the vicmodem and a denialesque BBS to walk aside me in my journey.

Thanks,
Piranger

[chysn]

I still don't see how to change just 900F. I tried M 900F,900F but that still displays the whole line. I also tried typing over all 5 registers on the line and still get a full cyan screen. I'm missing the trick of showing just 1 memory value.

To change a single value, supply only a single parameter after the address:

Code: Select all

.:900F 08

[piranger]

ahhhh...yes! that worked!

thanks,

Piranger