Custom Chip Registers

Custom chip registers are used for interacting with the custom chips on the Amiga. Some registers are read-only, others are write-only; care must be taken to respect. Undefined bits should always be cleared when writing, and other bits should be left in their current state to avoid upsetting other functions.

You will notice that all registers are contained within the 4KB address range $DFFxxx. Often the addresses are documented as a 12-bit address, in which case the $DFF prefix is assumed.

Unless otherwise stated, all accesses are 16-bit words.

Address	Register	Read/Write	Chip	OCS	ECS	AGA	Function
DFF09E	ADKCON	W	Paula	✓	✓	✓	Audio, disk, control write
DFF010	ADKCONR	R	Paula	✓	✓	✓	Audio, disk, control read
DFF0A0	AUD0LCH	W	Agnus	✓	✓*	✓	Audio channel 0 location (high 3 bits, 5 bits if ECS)
DFF0A2	AUD0LCL	W	Agnus	✓	✓	✓	Audio channel 0 location (low 15 bits)
DFF0A4	AUD0LEN	W	Paula	✓	✓	✓	Audio channel 0 length
DFF0A6	AUD0PER	W	Paula	✓	✓*	✓	Audio channel 0 period
DFF0A8	AUD0VOL	W	Paula	✓	✓	✓	Audio channel 0 volume
DFF0AA	AUD0DAT	W	Paula	✓	✓	✓	Audio channel 0 data
DFF0B0 - DFF0DA	Repeat of Channel 0 audio registers, DFF0Bx for channel 1, DFF0Cx for channel 2, DFF0Dx for channel 3

* Changes were made starting with this revision of chip. See Hardware Reference Manual for details.

A full list of custom chipset registers can be found at http://coppershade.org/articles/Code/Reference/Custom_Chip_Register_List/