KARNAK

The KARNAK mapper is only used in some Pocket Challenge V2 edutainment cartridges.

It is not yet well-documented. It is thought to be a revision of Bandai 2003 that removes the RTC interface, and adds a timer IRQ and a hardware IMA ADPCM decoder.

This page should not be taken as authoritative: it has been pieced together from multiple other pieces of research. It is unclear if the GPO and Self-Flash registers exist; from PCB photos the Self-Flash register is unused if it does exist.

Category	Port	Description	Bits	Type	Notes
GPO	$CC	GPO Data Direction	0000 oooo	RW8	1 = output, 0 = high-impedance (weak pull-down)
	$CD	GPO Data	0000 dddd	RW8	1 = 3V, if enabled by data direction
Self-Flash	$CE	Self-Flash Control	0000 000r	RW8	1 = ROM is accessible at segment 0x1000; 0 = RAM instead.
Extended bankswitching	$CF	ROM Linear (EX) Bank	00bb bbbb	RW8	Selects a 1MiB bank accessed via segments 0x4000 through 0xF000. Identical to the register at 0xC0.
	$D0	RAM(/ROM) Bank	0000 00bb bbbb bbbb	RW16	Selects a 64KiB bank accessed via segment 0x1000. Lower 8 bits are identical to the register at 0xC1.
	$D2	ROM0 Bank	0000 00bb bbbb bbbb	RW16	Selects a 64KiB bank accessed via segment 0x2000. Lower 8 bits are identical to the register at 0xC2.
	$D4	ROM1 Bank	0000 00bb bbbb bbbb	RW16	Selects a 64KiB bank accessed via segment 0x3000. Lower 8 bits are identical to the register at 0xC3.
Timer	$D6	Programmable Interval Timer	eppp pppp	RW8	Enable (e); Period (p). Units are the 384kHz clock to the cartridge.
ADPCM	$D8	Packed data	?	W8?	Write two-sample packed ADPCM byte
	$D9	Unpacked data	?	R8?	Read two one-byte unpacked PCM bytes, in sequence

Timer

If enabled, the timer will emit a cartridge interrupt every ((period + 1) * 2) cartridge clocks, where "one cartridge clock" = 384KHz = 1/8th CPU clock.