Meet the Machine · Lesson 1 of 30 · about 5 minutes

Your First Emoji Program

Move a number into the CPU, print it, and stop.

01 / Explain

Understand the idea

A program is an ordered list of instructions. Our CPU fetches the instruction at its program counter (PC), executes it, and usually advances to the next instruction. The editor shows source lines; the PC counts compiled instructions starting at zero. Comments and blank lines do not count.

📥 LOAD puts a number in register R0. 🖨️ PRINT copies R0 to the output console. ⏹️ HALT stops execution. Emoji and their English keyboard mnemonics are two ways to write exactly the same machine instruction.

02 / Try

Watch it happen

Step three times. Watch PC 0 → 1 → 2, R0 become 42, and one output appear. HALT leaves PC at its own instruction.

📥 42
🖨️
⏹️

Use Step to follow one instruction at a time. You can change the example and replay it.

03 / Challenge

Make it work

Write a program that prints 42 exactly once and halts. Use LOAD, PRINT, and HALT.

The checker runs your current editor program in a fresh machine for each of 1 test cases. It supplies inputs and seeded memory itself; the lab’s current output and memory do not decide your result.

# Put 42 in R0, print it, then stop.
HALT

Need a hint?

PRINT reads R0; put the value there first.

Reveal a worked solution

Read the program, predict each instruction’s effect, then step through it in the lab.

LOAD 42
PRINT
HALT

Emoji program

Type LOAD, ADD, or another opcode then Space to insert emoji. Ctrl/⌘ + Enter runs or pauses; Escape pauses; Ctrl/⌘ + ] indents. Tab moves focus. Labels use a colon. Jumps use zero-based instruction addresses.

# Put 42 in R0, print it, then stop.
HALT

Instruction map and breakpoints (0)

Breakpoints stop before an instruction. Run resumes past the stopped breakpoint once; Step executes it directly. Editing source clears old breakpoints and machine state.

Use Number

CPU registers

R0: 0
R1: 0
R2: 0
R3: 0
R4: 0
R5: 0
R6: 0
R7: 0

Program counter (PC): 0
Stack pointer (SP): 255
Flags: Zero: off · Negative: off · Overflow: off
Delay request: 0 ms

Stacks and loop frames

SP = 255 − data depth − call depth. The stack is separate from memory.

Data stack (bottom → top)

Empty

Call return addresses (bottom → top)

Empty

Loop frames

Empty

Output and input

Run a PRINT instruction to see output.

Queued input: Empty

Memory · 256 bytes · 0 nonzero

Each cell shows address:value. R = read this step; W = written this step. Select a cell to inspect or initialize it before execution. Use arrow keys to move, Home/End for the row, and Ctrl/⌘ + Home/End for the whole memory.

Execution trace · 0 entries

Recent entries below. Inspect any zero-based index to see complete detached before/after state.

Check your challenge

You can run this check any time. Every case must pass to record completion.

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