[Coco] Assembly help: Corrupted bin file ?

[Fedor Steeman]

Hi Robert,

Thanks! I tried your suggestions and they give me what I want. I have been
trying to figure exactly what these extra lines do.

 STA  $FFC7
 STA  $FFC9
 STA  $FFCB

I have found an awesome hardware reference on the internet by Chris Lomont (
http://www.lomont.org/Software/Misc/CoCo/Lomont_CoCoHardware.pdf) that
helped a bit, but not quite yet.

 This is what it says:

ffc6/ffc7 SAM Display Offset bit F0
ffc8/ffc9 SAM Display Offset bit F1
ffca/ffcb SAM Display Offset bit F2

What exactly is meant with offset and why must it be set three places?
Thanks for any hints. I am aware that I must strik you all as a bit
clueless. :-)

Cheers,
Fedor


I've mounted the program on a disk and used LOADM and EXEC to run it. It
> does exactly what you asked it to although that might not be what you really
> want.
> The first thing I see is the PMODE4 screen with alternate black and white
> vertical lines. I also see a short horizontal black line in the upper left
> quadrant. That is undoubtedly the result of your choice for the location of
> the PMODE4 screen at $400.
> That is not a good location for a PMODE4 screen because you overlap part of
> the disk operating system in low RAM. $400 is the location of the low res
> text screen from $400-$5FF. The PMODE4 screen should start at $E00 or higher
> on a disk system.
> The first key press results in a low res text screen filled with vertical
> blue and black lines with the exception of the last two horizontal lines
> which are default green with OK on the second to last line.
> This is also expected because you put graphics data on the text screen.
>
> You should change your code as follows:
> VIDRAM EQU $E00
> VOFS1  EQU $FFC7
> VOFS2  EQU $FFC9
> VOFS3  EQU $FFCB
>
> Change the program origin to:
>  ORG $7000
>
>  CMPX #$1C00  replace with
>  CMPX #VIDRAM+$1800
>
>  STA  VOFSET  replace with
>  STA  VOFS1
>  STA  VOFS2
>  STA  VOFS3
>
> See how the program works after the above changes.
>
>
> --
> Coco mailing list
> Coco at maltedmedia.com
> http://five.pairlist.net/mailman/listinfo/coco
>