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		<h1><a href="index.html">Emulator Development</a></h1>
		<div class="description">The art of emulator programming</div>
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			<div class="alignleft">&laquo; <a href="index2df4.html?p=8">Gameboy emulator 95% compatibility</a></div>
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			<h2>Starting the Master System</h2>

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				<p>Over the past few days I&#8217;ve had a few hours spare to start reading about the sega master system. The CPU is a Z80 which is what the Gameboy CPU is similar to, so I have already implemented 50% of the instructions. I have found the website <a href="http://www.smspower.org/dev/docs/">SMS Power</a> very useful for the SMS documentation. Unlike the gameboy there is not one document which covers everything you need to emulate the SMS so I&#8217;m using about 7 different resources to learn from, which I quite like doing really as it feels less spoon fed this way.</p>
<p>When I first started looking into emulating the Z80 I thought it would be easier than the Gameboy because of the fewer interupts and I found the gameboy quite quirky, however this is not the case. The other 50% of the Z80 cpu instructions I have to implement are more complicated than the 50% I&#8217;ve already implemented. Plus there are another 5 flags that need to be set correctly. The 0xFD and 0xDD opcodes make the cpu feel quite bloated aswell. The VDP seems much more complicated than the Gameboy and so do the way the interupts work. I&#8217;m still confident that I can finish this system in two months including sound but only if I have the time to do work on it, but it wont be as easy as I first thought.</p>
<p>I have got a few test roms from that SMS Power site which I have emulated all the opcodes for, so now I just need to get the VDP showing something for them. Once I have emulated the VDP I should be able to run ZEXALL which is a Z80 test rom, which will be really usefull for eliminating cpu bugs.</p>
<p>Fun fun fun</p>

								
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