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https://github.com/ekeeke/Genesis-Plus-GX.git
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65 lines
2.3 KiB
C
65 lines
2.3 KiB
C
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/* this defines the type of EEPROM inside the game cartridge as Backup RAM
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* Here are some notes from 8BitWizard (http://www.spritesmind.net/_GenDev/forum):
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*
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* Mode 1 (7-bit) - the chip takes a single byte with a 7-bit memory address and a R/W bit (24C01)
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* Mode 2 (8-bit) - the chip takes a 7-bit device address and R/W bit followed by an 8-bit memory address;
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* the device address may contain up to three more memory address bits (24C01 - 24C16).
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* You can also string eight 24C01, four 24C02, two 24C08, or various combinations, set their address config lines correctly,
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* and the result appears exactly the same as a 24C16
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* Mode 3 (16-bit) - the chip takes a 7-bit device address and R/W bit followed by a 16-bit memory address (24C32 and larger)
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*
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* Also, while most 24Cxx are addressed at 200000-2FFFFF, I have found two different ways of mapping the control lines.
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* EA uses SDA on D7 (read/write) and SCL on D6 (write only), and I have found boards using different mapping (I think Accolade)
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* which uses D1-read=SDA, D0-write=SDA, D1-write=SCL. Accolade also has a custom-chip mapper which may even use a third method.
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*/
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typedef struct
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{
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uint8 address_bits; /* number of bits needed to address the array: 7, 8 or 16 */
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uint16 size_mask; /* size of the array (in bytes) - 1 */
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uint16 pagewrite_mask; /* maximal number of bytes that can be written in a single write cycle - 1*/
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uint32 sda_in_adr; /* 68k address used by SDA_IN signal */
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uint32 sda_out_adr; /* 68k address used by SDA_OUT signal */
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uint32 scl_adr; /* address used by SCL signal */
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uint8 sda_in_bit; /* position of the SDA_IN bit */
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uint8 sda_out_bit; /* position of the SDA_OUT bit */
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uint8 scl_bit; /* position of the SCL bit */
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} T_EEPROM_TYPE;
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typedef enum
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{
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STAND_BY = 0,
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WAIT_STOP,
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GET_SLAVE_ADR,
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GET_WORD_ADR_7BITS,
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GET_WORD_ADR_HIGH,
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GET_WORD_ADR_LOW,
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WRITE_DATA,
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READ_DATA,
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} T_EEPROM_STATE;
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typedef struct
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{
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uint8 sda;
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uint8 scl;
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uint8 old_sda;
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uint8 old_scl;
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uint8 cycles;
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uint8 rw;
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uint16 slave_mask;
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uint16 word_address;
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T_EEPROM_STATE state;
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T_EEPROM_TYPE type;
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} T_EEPROM;
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/* global variables */
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extern T_EEPROM eeprom;
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/* Function prototypes */
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extern void EEPROM_Init();
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extern void EEPROM_Write(unsigned int address, unsigned int value);
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extern unsigned int EEPROM_Read(unsigned int address);
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