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bag-of-chips

CHIP-8

Especificación hardware

• Memoria: Acceso directo hasta 4KiB de RAM.
• Display: Pantalla monocroma de 64 x 32 píxeles (128 x 64 para SUPER-CHIP).
• Registros:

Reg	Resolución	Función
PC	16 bit	Contador de programa
I	16 bit	Registro índice
V0-F	8 bit	Registros de propósito general
VF	8 bit	Registro de flags

• Pila con direccionamiento de 16 bits.
• Temporizador de 8 bits que se decrementa 60 veces por segundo hasta que llega a 0.
• Temporizador de 8 bits que funciona como el anterior, pero si distinto de 0 pita.
• Keypad de 16 botones (4 x 4).

Opcodes

(from https://github.com/trapexit/chip-8_documentation)

Opcode	Mnemonic	Origin/Version	Description
001N	EXIT N	CHIP-8	From Peter Miller’s chip8run. Exit emulator with a return value of `N`.
00BN	SCU N	SCHIP-8	Scroll display `N` lines up.
00CN	SCD N	SCHIP-8	Scroll display `N` lines down.
00E0	CLS	CHIP-8	Clears the display. Sets all pixels to `off`.
00EE	RET	CHIP-8	Return from subroutine. Set the `PC` to the address at the top of the stack and subtract `1` from the `SP`.
00FA	COMPAT	CHIP-8	Non-standard. Toggles changing of the `I` register by `save (FX55)` and `restore (FX65)` opcodes.
00FB	SCR	SCHIP-8	Scroll display `4` pixels to the right.
00FC	SCL	SCHIP-8	Scroll display `4` pixels to the left.
00FD	EXIT	SCHIP-8	Exit the interpreter.
00FE	LOW	SCHIP-8	Enable low res (64x32) mode.
00FF	HIGH	SCHIP-8	Enable high res (128x64) mode.
0NNN	CALL NNN	CHIP-8	Call machine language subroutine at address `NNN`.
02A0	STEPCOL	CHIP-8X	Steps background 1 color (-> blue -> black -> green -> red ->)
1NNN	JMP NNN	CHIP-8	Set `PC` to `NNN`.
2NNN	CALL NNN	CHIP-8	Call subroutine a `NNN`. Increment the `SP` and put the current `PC` value on the top of the stack. Then set the `PC` to `NNN`. Generally there is a limit of 16 successive calls.
3XNN	SE VX, NN	CHIP-8	Skip the next instruction if register `VX` is equal to `NN`.
4XNN	SNE VX, NN	CHIP-8	Skip the next instruction if register `VX` is **not** equal to `NN`.
5XY0	SE VX, VY	CHIP-8	Skip the next instruction if register `VX` equals `VY`.
5XY1	SGT VX, VY	CHIP-8E	Skip the next instruction if register `VX` is greater than `VY`.
5XY1	ADD VX, VY	CHIP-8X	Let `VX = VX + VY` (hex digits 00 to 77) (useful for manipulating the `NH, NV` parameters for low resolution color.)
5XY2	SLT VX, VY	CHIP-8E	Skip the next instruction if register `VX` is less than `VY`.
5XY3	SNE VX, VY	CHIP-8E	Skip the next instruction if register `VX` does not equal `VY`.
6XNN	LD VX, NN	CHIP-8	Load immediate value `NN` into register `VX`.
7XNN	ADD VX, NN	CHIP-8	Add immediate value `NN` to register VX. Does **not** effect `VF`.
8XY0	LD VX, VY	CHIP-8	Copy the value in register `VY` into `VX`
8XY1	OR VX, VY	CHIP-8	Set `VX` equal to the bitwise `or` of the values in `VX` and `VY`.
8XY2	AND VX, VY	CHIP-8	Set `VX` equal to the bitwise `and` of the values in `VX` and `VY`.
8XY3	XOR VX, VY	CHIP-8	Set `VX` equal to the bitwise `xor` of the values in `VX` and `VY`. **Note:** This instruction was originally undocumented but functional due to how the 8XXX instructions were implemented on teh COSMAC VIP.
8XY4	ADD VX, VY	CHIP-8	Set `VX` equal to `VX` plus `VY`. In the case of an overflow `VF` is set to `1`. Otherwise `0`.
8XY5	SUB VX, VY	CHIP-8	Set `VX` equal to `VX` minus `VY`. In the case of an underflow `VF` is set `0`. Otherwise `1`. (`VF = VX > VY`)
8XY6	SHR VX, VY	CHIP-8	Set `VX` equal to `VX` bitshifted right `1`. `VF` is set to the least significant bit of `VX` prior to the shift. Originally this opcode meant set `VX` equal to `VY` bitshifted right `1` but emulators and software seem to ignore `VY` now. **Note:** This instruction was originally undocumented but functional due to how the 8XXX instructions were implemented on teh COSMAC VIP.
8XY7	SUBN VX, VY	CHIP-8	Set `VX` equal to `VY` minus `VX`. `VF` is set to `1` if `VY` > `VX`. Otherwise `0`. **Note:** This instruction was originally undocumented but functional due to how the 8XXX instructions were implemented on teh COSMAC VIP.
8XYE	SHL VX, VY	CHIP-8	Set `VX` equal to `VX` bitshifted left `1`. `VF` is set to the most significant bit of `VX` prior to the shift. Originally this opcode meant set `VX` equal to `VY` bitshifted left `1` but emulators and software seem to ignore `VY` now. **Note:** This instruction was originally undocumented but functional due to how the 8XXX instructions were implemented on teh COSMAC VIP.
9XY0	SNE VX, VY	CHIP-8	Skip the next instruction if `VX` does **not** equal `VY`.
9XY1	MUL VX, VY	CHIP-8E	Set `VF`, `VX` equal to `VX` multipled by `VY` where `VF` is the most significant byte of a 16bit word.
9XY2	DIV VX, VY	CHIP-8E	Set `VX` equal to `VX` divided by `VY`. `VF` is set to the remainder.
9XY3	BCD VX, VY	CHIP-8E	Let `VX`, `VY` be treated as a 16bit word with `VX` the most significant part. Convert that word to BCD and store the 5 digits at memory location `I` through `I+4`. `I` does not change.
ANNN	LD I, NNN	CHIP-8	Set `I` equal to `NNN`.
BNNN	JMP V0, NNN	CHIP-8	Set the `PC` to `NNN` plus the value in `V0`.
B0NN	OUT NN	CHIP-8I	Output `NN` to port.
B1X0	OUT VX	CHIP-8I	Output contents of `VX` to port.
B1X1	IN VX	CHIP-8I	Read input from port and palce in `VX`.
BXY0	COL VX, VY	CHIP-8X	Set `VY` color @ `VX(NH)`, `VX+1(NV)` (provides low resolution color 8x8.)
BXYN	COL VX, VY, N	CHIP-8X	`N != 0`, set `VY` color @ `VX`, `VX+1` byte `N` bytes vertically (provides high resolution 8x32.)
CXNN	RND VX, NN	CHIP-8	Set `VX` equal to a random number ranging from `0` to `255` which is logically `and`ed with `NN`.
DXY0	DRW VX, VX, 0	SCHIP-8	When in high res mode show a `16x16` sprite at `(VX, VY)`.
DXYN	DRW VX, VY, N	CHIP-8	Display `N`-byte sprite starting at memory location `I` at `(VX, VY)`. Each set bit of `xor`ed with what’s already drawn. `VF` is set to `1` if a collision occurs. `0` otherwise.
EX9E	SKP VX	CHIP-8	Skip the following instruction if the key represented by the value in `VX` is pressed.
EXA1	SKNP VX	CHIP-8	Skip the following instruction if the key represented by the value in `VX` is **not** pressed.
EXF2	SKP2 VX	CHIP-8X	Skip the following instruction if the key represented by the value in `VX` is pressed on hex keyboard 2.
EXF5	SKNP2 VX	CHIP-8X	Skip the following instruction the the key represented by the value in `VX` is **not** pressed on hex keyboard 2.
FX07	LD VX, DT	CHIP-8	Set `VX` equal to the `delay timer`.
FX0A	LD VX, KEY	CHIP-8	Wait for a key press and store the value of the key into `VX`.
FX15	LD DT, VX	CHIP-8	Set the delay timer `DT` to `VX`.
FX18	LD ST, VX	CHIP-8	Set the sound timer `ST` to `VX`.
FX1E	ADD I, VX	CHIP-8	Add `VX` to `I`. `VF` is set to `1` if `I > 0x0FFF`. Otherwise set to `0`.
FX29	LD I, FONT(VX)	CHIP-8	Set `I` to the address of the CHIP-8 8x5 font sprite representing the value in `VX`.
FX30	LD I, FONT(VX)	SCHIP-8	Set `I` to the address of the SCHIP-8 16x10 font sprite representing the value in `VX`.
FX33	BCD VX	CHIP-8	Convert that word to BCD and store the 3 digits at memory location `I` through `I+2`. `I` does not change.
FX55	LD [I], VX	CHIP-8	Store registers `V0` through `VX` in memory starting at location `I`. `I` does not change. ’
FX65	LD VX, [I]	CHIP-8	Copy values from memory location `I` through `I + X` into registers `V0` through `VX`. `I` does not change.
FX75	DISP VX	CHIP-8E	Display the value of `VX` on the COSMAC Elf hex display.
FX75	LD R, VX	SCHIP-8	Store `V0` through `VX` to HP-48 RPL user flags (X <= 7).
FX85	LD VX, R	SCHIP-8	Read `V0` through `VX` to HP-48 RPL user flags (X <= 7)
FX94	LD I, VX	CHIP-8E	Load `I` with the address of the font sprite of the `ASCII` value found in `VX`.
FXFB	IN VX	CHIP-8X	Copy contents from `input port` to `VX`. (Waits for EF4=1)
FXF8	OUT VX	CHIP-8X	Output contents of `VX` to `output port`. Used to program simple sound.

Documentación de apoyo

Iré actualizando esto a la que vaya viendo artículos nuevos:

• https://github.com/trapexit/chip-8_documentation
• http://mattmik.com/files/chip8/mastering/chip8.html
• https://chip-8.github.io/extensions/
• https://courses.ece.cornell.edu/ece5990/ECE5725_Fall2016_Projects/Lab_group_bcp39_rk534/cpu.html
• http://www.pong-story.com/chip8/
• https://www.zophar.net/pdroms/chip8/chip-8-games-pack.html
• https://johnearnest.github.io/chip8Archive/
• https://tobiasvl.github.io/blog/write-a-chip-8-emulator/