User:Zzo38/Mapper F

Registers

Registers are mapped at $5800-$5FFF, using the low four bits as a register number. There may be different registers for reading as for writing. The same registers are also mapped at $1800-$1FFF, however reading from those address may result in bus conflicts. Writing there is OK, though.

Therefore, the address mask is:

[0.01 1... .... xxxx]

$5800 (W)

[ESMM CCCC]
 |||| ||||
 |||| ++++--- CIRAM enable
 ||++-------- Nametable mirroring
 |+---------- CIRAM swap
 +----------- Enable console audio

If the "E" bit is cleared, then only the expansion audio is played, and the audio from 2A03 + microphone is disabled.

Nametable mirroring decides the connection of CIRAM A10, depending on "MM", and then that address line is XORed by "S", as follows:

• 00 = PA10
• 01 = PA11
• 10 = PA12
• 11 = PA13

The "CCCC" decides which sections of PPU address space are accessing CIRAM (if the bit is clear, CIRAM is used; if set, the CHR ROM/RAM in the cartridge is used):

• bit0 = $0000-$0FFF
• bit1 = $1000-$1FFF
• bit2 = $2000-$2FFF
• bit3 = $3000-$3EFF

$5800 (R)

[.... XXXX]
      ||||
      ++++--- 4-bit ADC

This register is a 4-bit ADC for the 2A03+microphone audio. Mute and expansion audio are not applied; it is the same audio signal as cartridge is receiving at first.

$5801 (W)

[VV.P PPPP]
 || | ||||
 || +-++++--- 16K PRG ROM bank at $8000-$BFFF
 ++---------- Video mode

$5802 (W)

[...P PPPP]
    | ||||
    +-++++--- 8K PRG ROM bank at $C000-$DFFF

This is actually the low 8K of a 16K bank, so the high 8K of a 16K bank cannot be mapped into $C000-$DFFF.

$5804

Same as register $580C, but for channel 1.

$5805

Same as register $580D, but for channel 1.

$5806

Same as register $580E, but for channel 1.

$5808

Same as register $580C, but for channel 2.

$5809

Same as register $580D, but for channel 2.

$580A

Same as register $580E, but for channel 2.

$580C (W)

[P..W AAAA]
 |  | ||||
 |  | ++++--- AND mask
 |  +-------- Waveform (0: saw, 1: square)
 +----------- Phase reset if bit is cleared

$580D (W)

[XXXX XXXX]
 |||| ||||
 ++++-++++--- Low bits of period of channel 3

$580E (W)

[XXXX XXXX]
 |||| ||||
 ++++-++++--- High bits of period of channel 3