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Chip8emu

CHIP-8 is an interpreted programming language developed by Joseph Weisbecker. It was used on the CoSMAC VIP and Telmac 1800 8-bit microcomputers in the mid-1970s.

Opcodes

Opcode Done Type Pseudocode Action
0NNN ign Call ignored by modern interpreters
00E0 ok Display Clears the screen
00EE ok Flow return Returns from a subroutine
1NNN ok Flow goto NNN Jump to Address NNN
2NNN ok Flow *(0xNNN)() Calls subroutine at NNN
3XNN ok Cond if(Vx==NN)() Skip the next instruction if Vx eq NN
4XNN ok Cond if(Vx!=NN) Skips next instruction if VX doesn't equal
5XY0 ok Cond if(Vx==Vy) Skips the next instruction if Vx equals Vy
6XNN ok Const Vx = NN Sets Vx to NN
7XNN ok Const Vx += NN Adds NN to VX. (Carry flag not changed)
8XY0 ok Assign Vx=Vy Sets VX to the value of VY
8XY1 ok BitOp Vx=Vx|Vy Sets VX to VX or VY
8XY2 ok BitOp Vx=Vx&Vy Sets VX to VX and VY
8XY3 ok BitOp Vx=Vx^Vy Sets VX to VX xor VY
8XY4 ok Math Vx += Vy Adds VY to Vx. VF is set to 1 if there is a carry, else to 0.
8XY5 ok Math Vx -= Vy VY is substracted from VX. VF is set to 0 when there's a borrow, and 1 when there isn't
8XY6 ok BitOp Vx >>= 1 Store the least significant bit of VX in VF and shift VX to right by 1
8XY7 ok Math Vx=Vy-Vx Set VX to VY minus VX. VF is set to 0 when there's a borrow
8XYE ok BitOp Vx<<=1 Store MSB of VX in VF and shift VX to left by 1
9XY0 ok Cond if(Vx!=Vy) Skip next instruction if VX doesn't equal VY
ANNN ok MEM 1 = NNN Sets I to the address of NNN
BNNN ok Flow PC=V0+NNN Jump to address NNN plus V0
CXNN ok Rand Vx=rand()&NN Sets Vx to the result of a bitwise and op. on a random number and NN
DXYN ok Disp draw(Vx,Vy,N) Dra sprite a coord (Vx,Vy) with width of 8 pix and hight of N pix.
EX9E ok KeyOp if(key()==Vx) Skips next instruction if key stored in VX is pressed
EXA1 ok KeyOp if(key()!=Vx) Skips the next instruction if the key sotred in Vx isn't pressed
FX07 ok Timer Vx=getdelay() Set Vx to the value of the delay timer
FX0A ok KeyOp Vx=getkey() A key press is awaited, then stored in VX. (Blocking)
FX15 ok Timer delaytimer(Vx) Set delay timer to Vx
FX18 ok Sound soundtime(Vx) Set sound timer to Vx
FX1E ok MEM I += Vx Adds VX to I.
FX29 ok MEM I = spriteaddr[Vx] Set I to location of srite for character in Vx, Chars 0-F are represented by a 4x5 font
FX33 tbt BCD Store binary-coded decimal rep of Vx at position I
FX55 tbt MEM regdump Store V0 to VX starting at I. offset from i is increased by 1 for each value
FX65 tbt MEM regload Fill V0 to Fx with values from memory starting at I. increase offset from I but do not touch I

Registers

The CHIP-8 has 16, 8-bit virtual registers: V0, V1, V2, V3, V4, V5, V6, V7, V8, V9, VA, VB, VC, VD, VE, VF. There is one single 16-bit register: I which is used for reading and writing to memory. There are two 8-bit timer registers that continuously count down at 60 Hz. The delay timer is good for time limiting the game of waiting brief periods. While the sound timer is non-zero a tone will be emitted. Contains 8 8bit user-flag registers R0-R7. Cannot be directly used, but registers V0-V7 can be saved and loaded from.

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