AX becomes CX
Keep MOV AX, 42 selected. Flip bit 0 in the first byte, the rightmost bit. B8 becomes B9; the low opcode bits now select CX.
Simulate and find CX = 002A. The immediate bytes did not change.
01 / BINARY PLAYGROUND
One bit.
A different instruction.
A small place to begin. Edit an instruction’s actual bytes, then observe what the supported model does to the registers.
CLICK OR PRESS SPACE ON A BIT TO FLIP IT · LEFTMOST = MOST SIGNIFICANT
Tab enters the bits once. Arrows move between bits/bytes; Home/End move within a byte, Ctrl/Cmd + Home/End across the instruction. Enter/Space toggles the focused bit.
MOV AX, 42
B8 2A 00Inspection context: 16-bit default.
THREE SMALL EXPERIMENTS
Change a destination.
Change a value.
42 becomes 43
Reset bits and CPU state. Flip bit 0 in the second byte: 2A becomes 2B. The following high byte remains 00.
Little-endian 2B 00 is 0x002B, decimal 43. AX receives the new value.
Flags remember a comparison
Reset, simulate MOV AX, 42, then select and simulate CMP AX, 42. AX stays at 42; ZF becomes 1 because the values are equal.
Selecting a new encoding preserves CPU state. “Reset CPU state” starts a fresh experiment.