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source/docs/eeprom.doc
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source/docs/eeprom.doc
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Here are some notes about EEPROM emulation, which is used in a few Sega Genesis Cartridge as external Backup RAM.
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The protocol used to communicate (read/write) with serial EEPROM is explained below:
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1/ from 68000 cpu (MASTER), which is running the ROM program, each EEPROM can be managed using only two single lines:
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- /SDA is the DATA line, used to send/receive data (READ/WRITE)
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- /SCL is the CLOCK line used to synchronize the EEPROM cycles (WRITE ONLY)
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2/ each line is mapped in the 68000 address space at a specific address as one specific bit (see game mappers below)
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and can be set at LOW (bit=0) or HIGH (bit=1) state.
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3/ each READ/WRITE operation must be initiated with a START condition and terminated by a STOP condition:
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- START condition is set when /SDA is changed from HIGH to LOW while /SCL remaining HIGH
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- STOP condition is set when /SDA is changed from LOW to HIGH while /SCL remaining HIGH
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4/ Following the START condition, the Master send one or more 8-bit word through the /SDA line to specify the address
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that must be read or write.
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Each bit write requires one clock cycle, managed by changing /SCL line state.
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There are 3 known EEPROM Modes, each one using different addressing protocol:
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- Mode 1 EEPROMs (24C01 only) have a maximal size of 128bytes (7bits address) and need only one address word.
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The 7 first bits specify the memory address to be read/write and the 8th bit indicates if the operation type (READ or WRITE)
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- Mode 2 EEPROMs (24C01 to 24C16) can be linked together (8 slave devices max.), that means in fact one 24C16, two 24C08, four 24C04,
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or eight 24C02/24C01, for a maximal size of 2 Kbytes (11bits address max.).
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A first word is needed: the first 4 bits are fixed and, depending on the EEPROM size, the next 3bits specify the device address
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and eventually the one (24C04), two (24C08) or three (24C16) upper bits of the memory address to be read/write.
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As before, the 8th bit specifies the type of the operation (READ or WRITE)
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Then a second word is needed to specify the eight lower bits of the address to be read/write.
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- Mode 3 EEPROMS (24C32 and more) work quite the Type 2 EEPROMS excepted that the maximal address size is 64 Kbytes (16bits address max.)
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The first word is like in the previous type, bits d3-d1 always specifying the slave device address (8 linked devices max.)
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The second word specifies the upper bits of the address to be read/write.
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A third word specifies the eight lower bits of the address to be read/write.
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NOTE: In Mode2 and Mode3, before a READ operation, only the SLAVE ADDRESS WORD will be sent, the EEPROM contains an address counter
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that maintains the address of the last word to be accessed (from a previous READ or WRITE operation)
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5/ Each time a 8bits word has been written (which requires eight clock cycles), the receiver (could be EEPROM or MASTER) send an acknowledge
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to the sender by setting /SDA line LOW during the 9th cycle (ACK cycle).
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6/ After a WRITE SEQUENCE has been initiated, the MASTER will sent DATA as one or more sequences of 8bits words.
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After each written word, the EEPROM must send a ACK and increment the address for the next data word to be written.
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Word address will roll up to base address when maximal writepage size has been reached.
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If the Master send a STOP condition, the WRITE operation ends.
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Otherwise the WRITE operation continues to next address.
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7/ After a READ SEQUENCE has been initiated, the MASTER will read DATA as one or more sequence of 8bits words.
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After each received word, the MASTER will send a ACK and the EEPROM will increment the address of the next data word to be read.
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Word address will roll up to 0 when maximal memory size has been reached.
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If the Master does not send a ACK during the 9th cycle, the READ operation ends and the EEPROM waits for STOP condition.
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Otherwise, the READ operation continue to next address.
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This is pretty how I emulate EEPROM access in Genesis Plus (see eeprom.c for technical details).
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Thanks a lot to 8bitWizard from Spriteminds.net forums which initially give indications about the various EEPROM types and mappers
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that can be found in Sega Genesis games.
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Here are some links to datasheets with should explain everything better than me and my crappy english ;)
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MODE1 (24C01 only):
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http://www.icmic.com/datasheets/X24C01.pdf
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MODE2 (24C01 - 24C16):
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http://www.atmel.com/dyn/resources/prod_documents/doc0180.pdf
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MODE3 (24C32 and more):
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http://www.phys.hawaii.edu/~bryce/component_data/24LC65-ISM.pdf
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Below are the Sega Genesis games that I found using serial EEPROM as external Backup RAM.
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I also give their specific caracteristics (mapper, size, ...), determined when testing my emulation code.
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EkeEke
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July 2007
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-------------------------------------------------------
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ACCLAIM (81)
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-------------------------------------------------------
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NBA Jam (UE)
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NBA Jam (J)
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------------
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T-081326
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T-81033
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header OK ($200001-$200001)
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TYPE: 8BITS WORD ADDRESS
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SIZE_MASK: 0xFF (24C02)
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PAGE_MASK: 0x03
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SDA_IN : 0x200000 (bit 0)
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SDA_OUT: 0x200000 (bit 1)
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SCL : 0x200000 (bit 1)
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NB: this game uses a different EEPROM mapper than any other Acclaim games.
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Blockbuster World Video Game Championship II (U)
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NBA Jam Tournament Edition (JUE)
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------------------------------------------------
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T-81406
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header KO
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TYPE: TYPE: 8BITS WORD ADDRESS
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SIZE_MASK: 0xFF (24C02)
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PAGE_MASK: 0x03
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SDA_IN : 0x200001 (bit 0)
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SDA_OUT: 0x200001 (bit 0)
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SCL : 0x200000 (bit 0)
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NB: Rev 00 of the game has buggy eeprom support and game backup does not seem to work fine, only Rev01
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version will correctly save game data.
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For history, Steve Snake, the author of Kega, one of the best Genesis emulator for Win32 platforms, is
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the one who originally developped this game.
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I assume that he released himself later some kind of patch to fix the backup support.
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(from the header informations, rev01 has been released in 2002, eight years after rev00 !)
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NFL Quarterback Club (JUE)
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-----------------------------
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T-081276
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header OK ($200000-$200001)
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TYPE: TYPE: 8BITS WORD ADDRESS
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SIZE_MASK: 0xFF (24C02)
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PAGE_MASK: 0x03
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SDA_IN : 0x200001 (bit 0)
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SDA_OUT: 0x200001 (bit 0)
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SCL : 0x200000 (bit 0)
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NFL Quarterback Club 96 (UE)
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-----------------------------
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T-081586
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header OK ($200000-$200001)
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TYPE: TYPE: 8BITS WORD ADDRESS
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SIZE_MASK: 0x7FF (24C16)
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PAGE_MASK: 0x07
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SDA_IN : 0x200001 (bit 0)
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SDA_OUT: 0x200001 (bit 0)
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SCL : 0x200000 (bit 0)
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College Slam (U)
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----------------
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T-81576
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header OK ($200001-$200001)
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TYPE: 16BITS WORD ADDRESS
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SIZE_MASK: 0x1FFF (24C64)
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PAGE_MASK: 0x07
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SDA_IN : 0x200001 (bit 0)
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SDA_OUT: 0x200001 (bit 0)
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SCL : 0x200000 (bit 0)
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Frank Thomas Big Hurt Baseball (UE)
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----------------
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T-81476
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header OK ($200000-$200001)
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TYPE: 16BITS WORD ADDRESS
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SIZE_MASK: 0x1FFF (24C64)
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PAGE_MASK: 0x07
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SDA_IN : 0x200001 (bit 0)
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SDA_OUT: 0x200001 (bit 0)
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SCL : 0x200000 (bit 0)
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-------------------------------------------------------
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CAPCOM (12)
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-------------------------------------------------------
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Megaman - The Wily Wars (E)
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Rockman Mega World (J) [alt]
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----------------
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T-12046
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T-12053 (checksum = 0xEA80)
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header OK ($200001-$200001)
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TYPE: 7BITS WORD ADDRESS
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SIZE_MASK: 0x7F (24C01)
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PAGE_MASK: 0x03
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SDA_IN : 0x200001 (bit 0)
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SDA_OUT: 0x200001 (bit 0)
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SCL : 0x200001 (bit 1)
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NOTE: the original version of Rockman Mega World (J) uses traditional SRAM, header gives $200000-$203FFF range
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the alternate version uses a 128bytes serial EEPROM (X24C01)
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the two versions share the same GAME NAME and PRODUCT ID
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-------------------------------------------------------
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Electronic Arts (50)
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-------------------------------------------------------
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NHLPA Hockey 93 (UE)
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----------------
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T-50396
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header KO
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TYPE: 7BITS WORD ADDRESS
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SIZE_MASK: 0x7F (24C01)
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PAGE_MASK: 0x03
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SDA_IN : 0x200000 (bit 7)
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SDA_OUT: 0x200000 (bit 7)
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SCL : 0x200000 (bit 6)
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Rings of Power (UE)
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----------------
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T-50176
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header KO
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TYPE: 7BITS WORD ADDRESS
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SIZE_MASK: 0x7F (24C01)
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PAGE_MASK: 0x03
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SDA_IN : 0x200000 (bit 7)
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SDA_OUT: 0x200000 (bit 7)
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SCL : 0x200000 (bit 6)
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-------------------------------------------------------
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SEGA
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-------------------------------------------------------
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Evander 'Real Deal' Holyfield's Boxing (JUE)
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----------------------------------
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MK-1215
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header OK ($200001-$200001)
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TYPE: 7BITS WORD ADDRESS
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SIZE_MASK: 0x7F (24C01)
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PAGE_MASK: 0x03
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SDA_IN : 0x200001 (bit 0)
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SDA_OUT: 0x200001 (bit 0)
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SCL : 0x200001 (bit 1)
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Greatest Heavyweights of the Ring (U)
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Greatest Heavyweights of the Ring (J)
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Greatest Heavyweights of the Ring (E)
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-----------------------------
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MK-1228
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G-5538
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PR-1993
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header OK ($200001-$200001)
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TYPE: 7BITS WORD ADDRESS
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SIZE_MASK: 0x7F (24C01)
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PAGE_MASK: 0x03
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SDA_IN : 0x200001 (bit 0)
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SDA_OUT: 0x200001 (bit 0)
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SCL : 0x200001 (bit 1)
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Wonder Boy in Monster World (UE)
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Wonder Boy V - Monster World III (J)
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----------------
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G-4060
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header OK ($200001-$200001)
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TYPE: 7BITS WORD ADDRESS
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SIZE_MASK: 0x7F (24C01)
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PAGE_MASK: 0x03
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SDA_IN : 0x200001 (bit 0)
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SDA_OUT: 0x200001 (bit 0)
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SCL : 0x200001 (bit 1)
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-------------------------------------------------------
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CODEMASTERS
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-------------------------------------------------------
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Micro Machines 2 - Turbo Tournament (E) (J-Cart)
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------------------------------------------------
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T-120096-50
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header KO
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TYPE: TYPE: 8BITS WORD ADDRESS
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SIZE_MASK: 0x3FF (24C08)
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PAGE_MASK: 0x0F
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SDA_IN : 0x300000 (bit 0)
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SDA_OUT: 0x380001 (bit 7)
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SCL : 0x300000 (bit 1)
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NB: this game needs the external RAM to be initialized with 0xFF otherwise it won't initialize memory with correct data.
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Micro Machines Military (E) (J-Cart)
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------------------------------------
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00000000-00 (checksum = 0x168B or 0xCEE0)
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header KO
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TYPE: TYPE: 8BITS WORD ADDRESS
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SIZE_MASK: 0x3FF (24C08)
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PAGE_MASK: 0x0F
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SDA_IN : 0x300000 (bit 0)
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SDA_OUT: 0x380001 (bit 7)
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SCL : 0x300000 (bit 1)
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Micro Machines Turbo Tournament 96 (E) (J-Cart)
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------------------------------------------------
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00000000-00 (checksum = 0x165E or 0x2C41)
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header KO
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TYPE: TYPE: 8BITS WORD ADDRESS
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SIZE_MASK: 0x7FF (24C16)
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PAGE_MASK: 0xF
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SDA_IN : 0x300000 (bit 0)
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SDA_OUT: 0x380001 (bit 7)
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SCL : 0x300000 (bit 1)
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@ -1,7 +1,7 @@
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/****************************************************************************
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* Serial EEPROM support for Sega Genesis games
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*
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* Copyright (C) 2007 EkeEKe
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* Copyright (C) 2007 EkeEke
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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@ -18,7 +18,7 @@
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*
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*
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* Freeze State support (added by EkeEke for the Gamecube's port - Feb,2007)
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* Freeze State support (added by EkeEke for Gamecube's port - Feb,2007)
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*
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***************************************************************************/
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#include "shared.h"
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