mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
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236 lines
5.8 KiB
HTML
236 lines
5.8 KiB
HTML
<HTML>
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<HEAD>
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<TITLE>GameGenie patches</TITLE>
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</HEAD>
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<BODY TEXT="#000000" BGCOLOR="#FEFEF4">
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<BASEFONT FACE="MS Sans Serif" SIZE="-1">
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<BR>
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<CENTER><H1>GameGenie Patching</H1></CENTER>
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<BR>
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<P> GameGenie was a device created by codemasters and galoob that
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let you make cheats for games. It was plugged in the console like a normal
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cartridge, and in its top the desired cartridge was plugged. These cheats are
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possible because what GameGenie do is edit the RAM that stores values used by
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the ROMs, setting these values to a constant that can be, for example, the
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number of lifes you have!</P>
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<P> Genecyst was the first Genesis emulator to have support
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for GameGenie then, with Kgen98, Steve Snake started to use this neat feature
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in his great emulator. No ROM image of a GameGenie is necessary, as some may
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imagine, to use them with console emulators, these programs themselves have a
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built-in feature that acts like a GameGenie, writing the codes in the emulated
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RAM.</P>
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<P> The GameGenie code consists of a eight-bytes long string, and
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the valid characters are A, B, C, D, E, F, G, H, J, K, L, M, N, P, R, S, T, V,
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W, X, Y, Z, 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9, all in uppercase. Each character
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have a binary repressentation, which is 5-bits long.</P>
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<TABLE WIDTH="70%" BORDER="0" ALIGN="CENTER">
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<TR>
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<TD>
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<TABLE BORDER="1" ALIGN="CENTER">
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<TR>
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<TH>Char</TH>
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<TH>Value</TH>
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</TR>
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<TR>
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<TD ALIGN="CENTER">A</TD><TD>00000</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">B</TD><TD>00001</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">C</TD><TD>00010</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">D</TD><TD>00011</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">E</TD><TD>00100</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">F</TD><TD>00101</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">G</TD><TD>00110</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">H</TD><TD>00111</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">J</TD><TD>01000</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">K</TD><TD>01001</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">L</TD><TD>01010</TD>
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</TR>
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</TABLE>
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</TD>
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<TD VALIGN="TOP">
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<TABLE BORDER="1" ALIGN="CENTER">
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<TR>
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<TH>Char</TH>
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<TH>Value</TH>
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</TR>
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<TR>
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<TD ALIGN="CENTER">M</TD><TD>01011</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">N</TD><TD>01100</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">P</TD><TD>01101</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">R</TD><TD>01110</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">S</TD><TD>01111</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">T</TD><TD>10000</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">V</TD><TD>10001</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">W</TD><TD>10010</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">X</TD><TD>10011</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">Y</TD><TD>10100</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">Z</TD><TD>10101</TD>
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</TR>
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</TABLE>
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</TD>
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<TD VALIGN="TOP">
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<TABLE BORDER="1" ALIGN="CENTER">
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<TR>
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<TH>Char</TH>
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<TH>Value</TH>
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</TR>
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<TR>
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<TD ALIGN="CENTER">0</TD><TD>10110</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">1</TD><TD>10111</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">2</TD><TD>11000</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">3</TD><TD>11001</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">4</TD><TD>11010</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">5</TD><TD>11011</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">6</TD><TD>11100</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">7</TD><TD>11101</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">8</TD><TD>11110</TD>
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</TR>
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<TR>
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<TD ALIGN="CENTER">9</TD><TD>11111</TD>
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</TR>
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</TABLE>
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</TD>
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</TR>
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</TABLE>
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<BR>
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<P> The cheat code should be firstly converted directly using the
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table above, and then the bits should be reordered. For example, the GameGenie
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code SCRA-BJX0 is translated to:</P>
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<FONT FACE="Courier">
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<TABLE BORDER="0" ALIGN="CENTER">
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<TR>
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<TD>
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<TABLE BORDER="0" ALIGN="CENTER">
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<TR><TD ALIGN="RIGHT" VALIGN="MIDDLE">Code:</TD></TR>
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<TR><TD ALIGN="RIGHT" VALIGN="MIDDLE">Bits:</TD></TR>
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<TR><TD ALIGN="RIGHT" VALIGN="MIDDLE">Id:</TD></TR>
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</TABLE>
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</TD>
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<TD>
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<TABLE BORDER="1" ALIGN="CENTER">
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<TR ALIGN="CENTER">
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<TD>S</TD><TD>C</TD><TD>R</TD><TD>A</TD>
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</TR>
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<TR ALIGN="CENTER">
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<TD>01111</TD><TD>00010</TD><TD>01110</TD><TD>00000</TD>
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</TR>
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<TR ALIGN="CENTER">
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<TD>ijklm</TD><TD>nopIJ</TD><TD>KLMNO</TD><TD>PABCD</TD>
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</TR>
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</TABLE>
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</TD>
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<TD>
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<TABLE BORDER="0" ALIGN="CENTER">
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<TR><TD ALIGN="RIGHT" VALIGN="MIDDLE">-</TD></TR>
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<TR><TD ALIGN="RIGHT" VALIGN="MIDDLE">-</TD></TR>
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<TR><TD ALIGN="RIGHT" VALIGN="MIDDLE">-</TD></TR>
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</TABLE>
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</TD>
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<TD>
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<TABLE BORDER="1" ALIGN="CENTER">
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<TR ALIGN="CENTER"><TD>B</TD><TD>J</TD><TD>X</TD><TD>0</TD></TR>
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<TR ALIGN="CENTER"><TD>00001</TD><TD>01000</TD><TD>10011</TD><TD>10110</TD></TR>
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<TR ALIGN="CENTER"><TD>EFGHd</TD><TD>efgha</TD><TD>bcQRS</TD><TD>TUVWX</TD></TR>
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</TABLE>
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</TD>
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</TR>
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</TABLE>
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</FONT>
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<P> Then rearrange (using the id) as...</P>
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<FONT FACE="Courier">
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<TABLE BORDER="0" ALIGN="CENTER">
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<TR>
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<TD>
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<TABLE BORDER="0" ALIGN="CENTER">
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<TR><TD ALIGN="RIGHT" VALIGN="MIDDLE">Bits:</TD></TR>
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<TR><TD ALIGN="RIGHT" VALIGN="MIDDLE">Id:</TD></TR>
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</TABLE>
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</TD>
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<TD>
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<TABLE BORDER="1" ALIGN="CENTER">
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<TR>
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<TD>00000000</TD><TD>10011100</TD><TD>01110110</TD>
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</TR>
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<TR ALIGN="CENTER">
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<TD>ABCDEFGH</TD><TD>IJKLMNOP</TD><TD>QRSTUVWX</TD>
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</TR>
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</TABLE>
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</TD>
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<TD>
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<TABLE BORDER="0" ALIGN="CENTER">
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<TR><TD ALIGN="RIGHT" VALIGN="MIDDLE">:</TD></TR>
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<TR><TD ALIGN="RIGHT" VALIGN="MIDDLE">:</TD></TR>
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</TABLE>
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</TD>
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<TD>
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<TABLE BORDER="1">
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<TR ALIGN="CENTER"><TD>01010100</TD> <TD>01111000</TD></TR>
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<TR ALIGN="CENTER"><TD>abcdefgh</TD><TD>ijklmnop</TD></TR>
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</TABLE>
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</TD>
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</TR>
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</TABLE>
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</FONT>
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<BR>
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<P> Which give us, in hexa, <B>009C76:5478</B>. This means that
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<B>H5478</B> will be written at <B>H009C76</B> memory offset.</P>
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</BODY>
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</HTML>
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