EEPROM
The WonderSwan utilizes M93LCx6-compatible EEPROMs:
- in the SoC:
- 1 Kbit internal EEPROM (M93LC46-compatible) on the WonderSwan,
- 16 Kbit internal EEPROM (M93LC86-compatible) on the WonderSwan Color,
- on cartridges:
- 1 Kbit cartridge EEPROM (M93LC46-compatible)
- 8 Kbit cartridge EEPROM (M93LC76-compatible)
- 16 Kbit cartridge EEPROM (M93LC86-compatible)
Additional variants exists which were not seen on any production cartridge:
- 2 Kbit EEPROM (M93LC56-compatible)
- 4 Kbit EEPROM (M93LC66-compatible)
Commands
READ - Read Word
The READ command takes an address of a word (address 0 => bytes 0, 1; address 1 => bytes 2, 3; ...) and returns the word at that address.
WRITE - Write Word
The WRITE command takes an address of a word (address 0 => bytes 0, 1; address 1 => bytes 2, 3; ...) and the word to write to it, then writes the word.
ERASE - Erase Word
The ERASE command takes an address of a word (address 0 => bytes 0, 1; address 1 => bytes 2, 3; ...) and erases the word at that address, setting it to 0xFFFF.
WDS - Write Disable
TODO
WRAL - Write All
TODO
ERAL - Erase All
TODO
WEN - Write Enable
TODO
I/O ports
The I/O ports listed refer to the internal EEPROM; for the cartridge EEPROM port numbers, refer to the mapper documentation.
Internal EEPROM Data ($BA, $BB)
15 bit 8 7 bit 0 ---- ---- ---- ---- dddd dddd dddd dddd |||| |||| |||| |||| ++++-++++--++++-++++- Data read from/written to the EEPROM.
This port functions as a shared buffer for both "read" and "write" modes. (TODO: Verify)
Internal EEPROM Command ($BC, $BD)
Command Pattern 1
15 bit 8 7 bit 0
---- ---- ---- ----
0000 0001 ooaa aaaa (1 Kbit - M93LC46)
0000 01oo aaaa aaaa (2, 4 Kbit - M93LC56/66)
0001 ooaa aaaa aaaa (8, 16 Kbit - M93LC76/86)
|||| |||| ||||
||++--++++-++++- Address (MSb .. LSb)
++-------------- Opcode:
01 - WRITE
10 - READ
11 - ERASE
Command Pattern 2
15 bit 8 7 bit 0
---- ---- ---- ----
0000 0001 00ss .... (1 Kbit - M93LC46)
0000 0100 ss.. .... (2, 4 Kbit - M93LC56/66)
0001 00ss .... .... (8, 16 Kbit - M93LC76/86)
||
++------------ Sub-Opcode:
00 - WDS
01 - WRAL
01 - ERAL
11 - WEN
Internal EEPROM Control ($BE, $BF write)
15 bit 8 7 bit 0
---- ---- ---- ----
.... .... pewr ....
||||
|||+------ 1 for READ command, 0 otherwise
||+------- 1 for WRITE and WRAL command, 0 otherwise
|+-------- 1 for ERASE, WDS, ERAL and WEN command, 0 otherwise
+--------- 1 to enable internal EEPROM write protection.
Cannot be cleared once set.
Internal EEPROM Status ($BE, $BF read)
15 bit 8 7 bit 0
---- ---- ---- ----
.... .... p... ..RD
| ||
| |+- 1 if a READ command has completed.
| +-- 0 if the EEPROM is busy,
| 1 if a command can be accepted (idle).
+--------- Internal EEPROM write protection:
0 = disabled, 1 = enabled
Hardware notes
EEPROM command bits are shifted out starting from the most significant bit of the port.
+----> EEPROM Serial Data
|
[0] <= [0000 0001 ooaa aaaa]
EEPROM Command Port
While the M93LCx6 family supports byte organization, the WonderSwan always uses word organization. As such, this implementation detail is omitted in this documentation.
