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

This command is not guaranteed to be present on all EEPROMs.

TODO

ERAL - Erase All

This command is not guaranteed to be present on all EEPROMs.

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.

Note that on the original/"mono" WonderSwan, the data and command registers can only be accessed word-wide via even addresses: access to odd addresses whether byte or word-wide don't provide valid data. This has been fixed on the WonderSwan Color, even for "mono" compatibility mode.

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 ....
            ||||
            |||+------ Read mode:  1 for READ command, 0 otherwise
            ||+------- Write mode: 1 for WRITE and WRAL command, 0 otherwise
            |+-------- Erase mode: 1 for ERASE, WDS, ERAL and WEN command, 0 otherwise
            +--------- 1 to enable internal EEPROM write protection.
                       Cannot be cleared once set. 

The mode flags control the behaviour of the EEPROM interface:

• Read mode: Sends 16 bits from Command, then reads 16 bits to Data.
• Write mode: Sends 16 bits from Command, then 16 bits from Data. De-asserts Microwire chip select, then re-asserts it and waits for the EEPROM to confirm command completion.
• Erase mode: Sends 16 bits from Command, de-asserts Microwire chip select, then re-asserts it and waits for the EEPROM to confirm command completion.

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

Internal EEPROM Layout

Offset	Length	Contents
$00	96	Program data. Can be written by programs even if write protection has been enabled.
$60	16	Owner name, custom character set.
$70	1	Owner birthday year, BCD, first/higher two digits
$71	1	Owner birthday year, BCD, last/lower two digits
$72	1	Owner birthday month, BCD
$73	1	Owner birthday day, BCD
$74	1	Owner gender: 0 - ? 1 - Male 2 - Female
$75	1	Owner blood type: 0 - ? 1 - A 2 - B 3 - AB 4 - 0
$76	Last booted cartridge developer/publisher ID
$77	Last booted cartridge game ID
$78	Last booted cartridge game version
$7C	Stored cartridge ID/version change counter
$7D	Owner name change counter
$7E	System startup counter
$83	Color console configuration
$84	Custom splash animation, if present

Owner name character set

	.0	.1	.2	.3	.4	.5	.6	.7	.8	.9	.A	.B	.C	.D	.E	.F
0.		0	1	2	3	4	5	6	7	8	9	A	B	C	D	E
1.	F	G	H	I	J	K	L	M	N	O	P	Q	R	S	T	U
2.	V	W	X	Y	Z	♥	♪	+	-	?	.

Color console configuration

7  bit  0
---- ----
sc.. ..vv
||     ||
||     ++- Volume level
|+-------- Contrast (WSC): 0 = Low, 1 = High
+--------- Custom splash animation 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.

Links

• STMicroelectronics M93LCx6 datasheet