Yhyno 2E: a silly 8-bit computer emulator

This is a tiny, minimalist 8-bit computer emulator I created for fun. The computer runs in your browser, has 208 bytes of user memory, and uses a fake tape reader as the main input. For output, it uses a simple control panel.

The input is interrupt-based: the computer will show "idle" when it's ready to accept input. Then, the input will overwrite the A register.

Memory Map

• 0x00 - 0xCF: User memory (208 bytes)
• 0xD0 - 0xFE: System code
• 0xFF: Memory index

Architecture

The computer has two registers:

• X: a general-purpose register, used to load from memory
• A: an arithmetic register (holds the results of operations), also used to save data to memory

There are also:

• Flags: Overflow, Equality (A = X)
• One-element stack for managing subroutine calls

Output

The output panel consists of three rows of 8 diodes each. They display the values of the X and A registers, as well as the current memory index, in binary.

The middle panel contains an overflow diode (A > 255), the "Idle" diode, showing whether the computer is waiting for input, and the "On" diode, showing the status of the clock.

Instruction Set

When writing your own instructions, you will need to use hex values. The following table contains the entire list of available instructions:

Opcode	Mnemonic	Description
0	WAIT	Wait for interrupt
1	SETX val	Set X to immediate value
2	LDX addr	Load from address into X
3	LDXA	Load into X from address indexed by A
4	SETA val	Set A to immediate value
5	STA addr	Store A in address
6	STAX	Store A in address indexed by X
7	ADD	A = A + X
8	AND	Bitwise AND (result in A)
9	XOR	Bitwise XOR (result in A)
A	ASL	Shift A left
B	ASR	Shift A right
C	GO addr	Jump to address (save return)
D	RET	Return from jump
E	JEQ addr	Jump if X = A (save return)
F	JOV addr	Jump if A overflows (save return)

Use

Loading and running instructions

To load from tape, press T, and then press "Load Tape". Then wait until the tape finishes loading (the diode switches off). The instructions will be written starting from the currently indexed address, so you can later use this fact to correct mistakes in your code. To execute loaded instructions starting from address 0x00, press E.

Editing code

To inspect user memory, press I. The A register will show the currently inspected address, and X will show the value. If you want to overwrite the value, you can write it on tape and load it, so it overwrites the current one. To move to the next address, press M. The X register will show the previous address, and A - the current one.

The "home" address of the system (so, where it is waiting for the user's input) is 0xEA. When writing programs, it is good to end them with a jump to that address: 0C, EA.