Subject: Re: [stella] New to 2600 Programming From: Ben Larson <wazzapfool@xxxxxxxxx> Date: Thu, 8 Nov 2001 06:47:24 -0800 (PST) |
--- core dump <core_dump_000@xxxxxxxxx> wrote: > Hi, > > I've been playing the Atari 2600 since I was a kid > and > the other night decided to get into programming. > I've > sort of touched Intel ASM before. I downloaded > several > manuals and text files, the DASM assembler, and a > sample program (How to Draw a Playfield). I've been > goofing around with the code and doing different > things. I noticed that the drawing of the playfield > occurs with .byte commands. What do the hex codes > mean, and how does the .byte command work, so I can > customize with my own colors and drawings? > > -core_dump I'm not sure exactly how familiar you are with assembly language programming, so sorry in advance if any of this sounds condescending. :) The '.byte' command you're seeing isn't an actual assembly instruction, it's just an instruction to the assembler itself. It tells the assembler that you want to reserve space at that location for one or more 8-bit values. In this way, you can allocate memory for data, although since this data is in read only memory, it can't be changed. Anyway, the values following the '.byte' directive tell the assembler what you want stored in these bytes you're allocating. In 'How To Draw a Playfield', the '.byte' command is used to store the data both for the playfield itself, and the playfield colors. The playfield data is just a series of monochrome bitmaps, more or less. Each byte of the playfield data holds a single line of data for either one or two of the letters that get displayed on-screen. Each byte of the color data, on the other hand, holds the color for an entire half-line of the playfield that gets displayed on screen. 'Stella.txt', which can be found on Nick Bensema's web site, explains the concepts behind this further... __________________________________________________ Do You Yahoo!? Find a job, post your resume. http://careers.yahoo.com ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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