Z80



The Z80 is a 8-bit little-endian CPU designed by Zilog.

It is used in NeoGeo systems as a sub-CPU to handle sound and music playback. It runs at 4MHz and only has access to the, the (or Z80 files), and its own RAM. It communicates with the CPU via a single-byte channel.

Because it doesn't share a RAM area with the 68k CPU like on the Sega Genesis, it can't be used efficiently to offload game computation tasks from the main CPU.

Also see:
 * Z80 port map
 * Z80 bankswitching



=Interrupts=


 * IRQs (address $38) are triggered by the YM2610 timers, if enabled.
 * An NMI (address $66) is triggered when the 68k sends a byte.

=Memory map=



Cartridge systems
Having a 16-bit address bus, the CPU allows access to 64KiB of memory at most. In NeoGeo cartridges, the or  chips provide a way to access more memory for M1 ROMs up to 4MiB. Four different switchable zones ("windows") are available.

The bank that appear in these windows are configured by reading from 4 of the Z80's ports (see page for explanation).

Bank offsets numbering depend on the window sizes:


 * Window 0 counts in 2KiB increments
 * Window 1 in 4KiB
 * Window 2 in 8KiB
 * Window 3 in 16KiB

On cartridge systems, all windows are initialized to 0 (verified on hardware). Many sound drivers start up by initializing the windows properly like indicated above.

For example, this code simply maps the Z80 $0000~$F7FF address range to M1 ROM $0000~$F7FF linearly, with no gaps.

ld   a,$1E in   a,($08)    ; Set window 0 at $1E*$800 = $F000 ld   a,$0E in   a,($09)    ; Set window 1 at $E*$1000 = $E000 ld   a,$06 in   a,($0A)    ; Set window 2 at $6*$2000 = $C000 ld   a,$02 in   a,($0B)    ; Set window 3 at $2*$4000 = $8000

Bank selection
The King of Fighters '97 does this:

rlca rlca ld   e,a ld   d,$00      ; DE = A * 4 (table entry size) ld   hl,$289C   ; Table address, see below add  hl,de ld   a,(hl) in   a,($08)    ; Set zone 0 inc  hl ld    a,(hl) in   a,($09)    ; Set zone 1 inc  hl ld    a,(hl) in   a,($0A)    ; Set zone 2 inc  hl ld    a,(hl) in   a,($0B)    ; Set zone 3
 * 32KiB bank number in A

The table at $289C is used to set the 4 zones like an unique $7800-bytes long one in 32KiB increments, meaning that $800 bytes are wasted at the end of each range (mapped to Z80 RAM).

Data at $289C:

1E 0E 06 02 = F000,  E000,  C000,  8000   "Big bank 0": $8000~ $F7FF   ($F800~ $FFFF  is wasted) 2E 16 0A 04 = 17000, 16000, 14000, 10000  "Big bank 1": $10000~$177FF  ($177FF~$17FFF is wasted) 3E 1E 0E 06 = 1F000, 1E000, 1C000, 18000  "Big bank 2": $18000~$1F7FF  ($1F7FF~$1FFFF is wasted) 4E 26 12 08 = 27000, 26000, 24000, 20000  "Big bank 3": $20000~$277FF  ($277FF~$27FFF is wasted) 5E 2E 16 0A = 2F000, 2E000, 2C000, 28000  "Big bank 4": $28000~$2F7FF  ($2F7FF~$2FFFF is wasted) 6E 36 1A 0C = 37000, 36000, 34000, 30000  "Big bank 5": $30000~$377FF  ($377FF~$37FFF is wasted) 7E 3E 1E 0E = 3F000, 3E000, 3C000, 38000  "Big bank 6": $38000~$3F7FF  ($3F7FF~$3FFFF is wasted)

Note that the game has a 128KiB M1 ROM, but the table is long enough to map up to 256KiB.

CD systems
CD systems only have 64KiB of RAM dedicated to the. There's no bankswitching.

It seems that allows loading Z80 files accross the whole range, and locks $0000~$F7FF as read-only to simulate ROM during execution.

=Pinout=



=Datasheet=

Z8400 datasheet: []