Meet the Machine · Lesson 2 of 30 · about 8 minutes
Understanding Registers
Use the eight fast workspaces without losing a value.
01 / Explain
Understand the idea
Registers R0 through R7 are the CPU’s fast workspaces. LOAD 17 R1 changes R1 without changing R0. LOAD R1 reads the value of R1 into R0; it does not read memory.
R0 is the accumulator: arithmetic and PRINT use it. COPY R1 R2 copies a register value while preserving the source. Changing any register with LOAD or COPY updates the flags from the copied value.
02 / Try
Watch it happen
Notice that R1 and R2 retain 17 while R0 changes from 99 to 17.
LOAD 17 R1
LOAD 99
COPY R1 R2
LOAD R2
PRINT
HALTUse Step to follow one instruction at a time. You can change the example and replay it.
03 / Challenge
Make it work
Keep 17 in R1 and copy it into R2. Print 17, then leave R0 at zero before halting. R1 and R2 must still hold 17.
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.
LOAD 17 R1
# Copy, print, then clear R0.
HALTNeed a hint?
Clearing R0 does not clear the other registers.
Reveal a worked solution
Read the program, predict each instruction’s effect, then step through it in the lab.
LOAD 17 R1
COPY R1 R2
LOAD R2
PRINT
LOAD 0
HALTEmoji CPU lab
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.
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.
CPU registers
- R0
- 0
- R1
- 0
- R2
- 0
- R3
- 0
- R4
- 0
- R5
- 0
- R6
- 0
- R7
- 0
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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