(all values in Hexadecimal unless stated)
The Chip-8 instruction set runs in 4k of memory (addresses 000 - FFF). Programs start at 200, memory before that containing the chip-8 interpreter on a real 1802 based machine. The screen is 64 x 32 (128 x 64 on superchip) and is monochrome. Their is a sound buzzer
There are 16 primary registers, called V0 - VF. VF is used for carries and borrows and shouldn't really be used as a general purpose register. There is a 12 bit index register called I. There is a program counter and stack pointer, but neither of these are accessible from program code.
There are 2 counters, the sound timer and the delay timer. Both count down at about 60Hz (on Chip8 they count down in threes using the PC's 18.2Hz Clock). When the sound timer is non-zero the buzzer sounds.
This is the Chip-8 Instruction set as I understand it....
NNN is an address
KK is an 8 bit constant
X and Y are two 4 bit constants
| Code | Assembler | Description | Notes |
| 00CN | scdown N | scroll the screen down N lines | SuperChip only |
| 00E0 | cls | clear the screen | |
| 00EE | rts | return from subroutine call | |
| 00FB | scright | scroll screen 4 pixels right | SuperChip only |
| 00FC | scleft | scroll screen 4 pixels left | SuperChip only |
| 00FE | low | disable extended screen mode | SuperChip only |
| 00FF | high | enable extended screen mode (128 x 64) | SuperChip only |
| 1NNN | jmp nnn | jump to address NNN | |
| 2NNN | jsr nnn | jump to subroutine at address NNN | 16 levels maximum |
| 3XRR | skeq vx,rr | skip next istruction if register VX == constant RR | |
| 4XRR | skne vx,rr | skip next intruction if register VX != constant RR | |
| 5XY0 | skeq vx,vy | skip next instruction if register VX == register VY | |
| 6XRR | mov vx,rr | move constant RR to register VX | |
| 7XRR | add vx,rr | add constant RR to register VX | No carry generated |
| 8XY0 | mov vx,vy | move register VY into VX | |
| 8XY1 | or vx,vy | or register VY with register VX, store result into register VX | |
| 8XY2 | and vx,vy | and register VY with register VX, store result into register VX | |
| 8XY3 | xor vx,vy | exclusive or register VY with register VX, store result into register VX | |
| 8XY4 | add vx,vy | add register VY to VX, store result in register VX, carry stored in register VF | |
| 8XY5 | sub vx,vy | subtract register VY from VX, borrow stored in register VF | register VF set to 1 if borrows |
| 8X06 | shr vx | shift register VX right, bit 0 goes into register VF | |
| 8XY7 | rsb vx,vy | subtract register VX from register VY, result stored in register VX | register F set to 1 if borrows |
| 8X0E | shl vx | shift register VX left, bit 7 stored into register VF | |
| 9XY0 | skne vx,vy | skip next instruction if register VX != register VY | |
| ANNN | mvi nnn | Load index register (I) with constant NNN | |
| BNNN | jmi nnn | Jump to address NNN + register V0 | |
| CXKK | rand vx,kk | register VX = random number AND KK | |
| DXYN | sprite vx,vy,n | Draw sprite at screen location (register VX,register VY) height N | Sprites stored in memory at location in index register (I), maximum 8bits wide. Wraps around the screen. If when drawn, clears a pixel, register VF is set to 1 otherwise it is zero. All drawing is XOR drawing (e.g. it toggles the screen pixels) |
| dry0 | xsprite rx,ry | Draws extended sprite at screen location rx,ry | Superchip only: As above,but sprite is always 16 x 16. |
| ek9e | skpr k | skip if key (register rk) pressed | The key is a key number, see the chip-8 documentation |
| eka1 | skup k | skip if key (register rk) not pressed | |
| fr07 | gdelay vr | get delay timer into vr | |
| fr0a | key vr | wait for for keypress,put key in register vr | |
| fr15 | sdelay vr | set the delay timer to vr | |
| fr18 | ssound vr | set the sound timer to vr | |
| fr1e | adi vr | add register vr to the index register | |
| fr29 | font vr | point I to the sprite for hexadecimal character in vr | Sprite is 5 bytes high |
| fr30 | xfont vr | point I to the sprite for hexadecimal character in vr | Superchip only: Sprite is 10 bytes high. |
| fr33 | bcd vr | store the bcd representation of register vr at location I,I+1,I+2 | Doesn't change I |
| fr55 | str v0-vr | store registers v0-vr at location I onwards | I is incremented to point to the next location on. e.g. I = I + r + 1 |
| fx65 | ldr v0-vr | load registers v0-vr from location I onwards | as above. |