MBC6

Overview

MBC6 (Memory Bank Controller 6) is an unusual MBC that contains two separately switchable ROM banks ($4000 and $6000) and RAM banks ($A000 and $B000), SRAM and an 8Mbit Macronix MX29F008TC-14 flash memory chip. It is only used in one game, Net de Get: Minigame @ 100, which uses the Mobile Adapter to connect to the web to download minigames onto the local flash.

0000-3FFF - ROM Bank 00 (Read Only)

Read-only access to ROM bank 0.

4000-5FFF - ROM/Flash Bank A 00-7F (Read/Write for flash, Read Only for ROM)

Read-only access to ROM and flash banks 00-7F, switchable independently from ROM/Flash Bank B. Only 8 kB (0x2000) is accessible at once in this bank, as opposed to the usual 16 kB.

6000-7FFF - ROM/Flash Bank B 00-7F (Read/Write for flash, Read Only for ROM)

Read-only access to ROM and flash banks 00-7F, switchable independently from ROM/Flash Bank A. Only 8 kB (0x2000) is accessible at once in this bank, as opposed to the usual 16 kB.

A000-AFFF - RAM Bank A 00-07 (Read/Write)

Read/write access to RAM banks 00-07, switchable independently from RAM Bank B. Only 4 kB (0x1000) is accessible at once in this bank, as opposed to the usual 8 kB.

B000-BFFF - RAM Bank B 00-07 (Read/Write)

Read/write access to RAM banks 00-07, switchable independently from RAM Bank A. Only 4 kB (0x1000) is accessible at once in this bank, as opposed to the usual 8 kB.

0000-07FF - RAM Enable (Write Only)

Mostly the same as for MBC1, a value of 0Ah will enable reading and writing to external RAM. A value of 00h will disable it.

0C00 - Flash Enable (Write Only)

Enable or disable access to the flash chip. Only the lowest bit (0 for disable, 1 for enable) is used. Flash Write Enable must be active to change this.

1000 - Flash Write Enable (Write Only)

Enable or disable write mode for the flash chip. Only the lowest bit (0 for disable, 1 for enable) is used. Note that this maps to the /WE pin on the flash chip, not whether or not writing to the bus is enabled; some flash commands (e.g. JEDEC ID query) still work with this off so long as Flash Enable is on.

2000-27FF - ROM/Flash Bank A Number (Write Only)

The number for the active bank in ROM/Flash Bank A.

2800-2FFF - ROM/Flash Bank A Select (Write Only)

Selects whether the ROM or the Flash is mapped into ROM/Flash Bank A. A value of 00 selects the ROM and 08 selects the flash.

3000-37FF - ROM/Flash Bank B Number (Write Only)

The number for the active bank in ROM/Flash Bank B.

3800-3FFF - ROM/Flash Bank B Select (Write Only)

Selects whether the ROM or the Flash is mapped into ROM/Flash Bank B. A value of 00 selects the ROM and 08 selects the flash.

Flash Commands

The flash chip is mapped directly into the A or B address space, which means standard flash access commands are used. To issue a command, you must write the value $AA to $5555 then $55 to $2AAA and, which are mapped as 2:5555/1:4AAA for bank A or 2:7555/1:6AAA for bank B followed by the command at either 2:5555/2:7555, or a relevant address, depending on the command.

The commands and access sequences are as follows, were X refers to either 4 or 6 and Y to 5 or 7, depending on the bank region:

2:Y555=$AA	1:XAAA=$55	2:Y555=$80	2:Y555=$AA	1:XAAA=$55	?:X000=$30	Erase sector* (set 8 kB region to $FFs)
2:Y555=$AA	1:XAAA=$55	2:Y555=$80	2:Y555=$AA	1:XAAA=$55	?:Y555=$10	Erase chip* (set entire flash to $FFs)
2:Y555=$AA	1:XAAA=$55	2:Y555=$90				ID mode (reads out JEDEC ID (C2,81) at $X000)
2:Y555=$AA	1:XAAA=$55	2:Y555=$A0				Program mode*
2:Y555=$AA	1:XAAA=$55	2:Y555=$F0				Exit ID/erase chip mode
2:Y555=$AA	1:XAAA=$55	?:X000=$F0				Exit erase sector mode
?:????=$F0						Exit program mode

Commands marked with * require the Write Enable bit to be 1. These will make the flash read out status bytes instead of values. A status of $80 means the operation has finished and you should exit the mode using the appropriate command. A status of $10 indicates a timeout.

Programming must be done by first erasing a sector, activating write mode, writing out 128 bytes (aligned), then writing a 0 to the final address to commit the write, waiting for the status to indicate completion, and writing 0xF0 to the final address again to exit program mode. If a sector is not erased first programming will not work properly. In some cases it will only allow the stored bytes to be anded instead of replaced; in others it just won't work at all. The only way to set the bits back to 1 is to erase the sector entirely. It is recommended to check the flash to make sure all bytes were written properly and re-write (without erasing) the 128 byte block if some bits didn't get set to 0 properly. After writing all blocks in a sector Flash Write Enable should be set to 0.

Source: [1]