Mode   3+                            
                                                                
Hi.  I  guess you've allready seen the 'demo' screen so you will
probally   have   a   good idea of what Mode 3+ is. It's a small
bit of code which not only allows you to have a full 128 colours
on  screen,  but  also allows you to have upto 16 colours on one
line. Yes! 16 differnt colours on one line! In Mode 3! Coo. Mode
3+  is basically a small routine which alters the colours during
the frame scan. This means that the mode can only really be used
for  displays  and things. Actually, there is a little processer
time left over. But not much.                                   
                                                                
I  won't  explain (=I can't be bothered) how the code works, but
take a look at the routine with a dissembler and read the bottom
of  page  17  of the tech' manual. Oh, and I know that XOR A (or
another  4T  instruction) then OUT (hmpr),A is faster than OUTI,
but  when  I tried it it didn't seem to make any difference. And
anyway,  OUTI  is  much better, as a loop can be used. Check out
the  way I did the loop however - It needed to be done like that
to keep the prog alined to the frame scan.                      
                                                                
Right, no more techincal bits. Promise. So what's all this about
16  colours on a line you ask? Is it just like Mode 4? Well, not
really.  More like Mode 2. In Mode 2 the screen is divided up in
to  8 by 1 cells, in which you can use 2 colours. In Mode 3+ the
cells  are  64  by  1 pixels, but in each you can use 4 colours.
That's  a  bit  crap  you may say, and perhaps you're right. But
used carefully, some nice screens could be produced. Oh  and the
4 colours you use must belong to the same 'set', by which I mean
they  must  belong  to  one  of the groups 0,1,2,3 or 4,5,6,7 or
8,9,10,11 or 12,13,14,15. That's even crapper you reply. But you
can change one palette colour each line. Happy?                 
                                                                
In other words, every 64 pixels along a mode 3 line (ie at x =  
0,64,128,192,256,320,384 and 448 you can use a differnt 'set' of
colous for the next 64 pixels), each line can use totally       
different colours to the other lines.                           
                                                                
So  how to you go about using Mode 3+? I made it fairly easy for
you.  This  program  takes two Mode 4 screens, and converts them
into  one  Mode  3+  screen. Simply select option 1, type in the
filenames,  and  any  palette changes you require, and a Mode 3+
screen will be produced. If you have used colours from more than
one  'set'  in  a single cell, the program will stop, the border
will  go  'liney',  and  you  should press space, then alter the
screen,  and  try  again.  Once  a  screen  has been sucessfully
created,  it  will  be  saved with a copy of the Mode 3+ display
routine.  To  display  the screen you will need to load (or poke
into  memory)  a  short  driver  program.  The  driver  code  is
auto-running,  so  you  need to load the screen first. Then load
the  driver. It may sound complicated, but break into the BASIC,
and  you  will  see  it's  quite  simple. When a screen is being
displayed, pressing any key will return you to BASIC. The driver
file has the filename "MODE3+.CD3".                             
                                                                
I  know  creating  screens  can be a bit awkward, but if Mode 3+
proves  popular,  perhaps  a DPaint - Mode 3+ converter could be
written?  I  found  the  Replace faciltity in the BLOCK2 menu of
FLASH! usefull when drawing Mode 3+ screens.