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This is a simple demonstration file for the Zeus assembler.
If you want more sustantial files they're available at www.desdes.com


Defining graphics characters.


This happens enough to be worth some support, so versions of Zeus after 2.10 understand a
DG pseudo-op which makes defining character sets easier; the format is probably best
described with examples:

This is a typical character defined using the binary prefix. I think you'd agree that without
the comments it would be hard to see what the character actually looked like...

                db %00010000 ;    *
                db %00111100 ;   ****
                db %01010000 ;  * *
                db %00111000 ;   ***
                db %00010100 ;    * *
                db %01111000 ;  ****
                db %00010000 ;    *
                db %00000000 ;

Using the DG pseudo-op can make this much clearer:

DG takes "." "_" or "-" as indicating a zero bit, and any other character (aside from comments
of course) as a one bit. It ignores spaces, use them for formatting if you like.

So, from v2.10 onwards that same character could be represented using DG as:

                dg ...x....
                dg ..xxxx..
                dg .x.x....
                dg ..xxx...
                dg ...x.x..
                dg .xxxx...
                dg ...x....
                dg ........

Or by:

                dg ...0....
                dg ..0000..
                dg .0.0....
                dg ..000...
                dg ...0.0..
                dg .0000...
                dg ...0....
                dg ........

Or by:

                dg ---X----
                dg --XXXX--
                dg -X-X----
                dg --XXX---
                dg ---X-X--
                dg -XXXX---
                dg ---X----
                dg --------

Or by:

                dg ___@____
                dg __@@@@__
                dg _@_@____
                dg __@@@___
                dg ___@_@__
                dg _@@@@___
                dg ___@____
                dg ________

And so on... Zeus won't allow you to use spaces for zero bits because doing so 
would make it impossible for Zeus to determine the character width, or to check
you hadn't missed a pixel. Right, now I have you believing that I'll admit it's
just that I couldn't be bothered to delve into the parser - it normally discards
spaces before the rest of the assembler gets to see them and if I wanted to use
spaces here I'd have to tell it not to do so...

If your character is more than 8-bits wide just carry on across the line, but you
MUST specify a mutiple of 8-bits or zeus will regard the definition as invalid.

                dg ______@@________
                dg ____@@@@@@@@____
                dg ___@@__@@_______
                dg ____@@@@@@______
                dg ______@@__@@____
                dg __@@@@@@@@______
                dg ______@@________
                dg ________________

The pixels in a byte are planted with the LHS as the most-significant bit, and
multiple bytes are planted LHS byte first. This is the format that most VDU's
and programmers would expect; if there are machines or applications out there
which would benefit substantially from a different format email me with details
and I may add the required options to support it.

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