CHIP-8

CHIP-8 is an interpreted programming language developed in the mid-1970s by Joseph Weisbecker for the COSMAC VIP and Telmac 1800 microcomputers. It was designed to make game programming easier. Programs are run on a virtual machine with a 64×32 pixel monochrome display, 16 input keys, and a simple sound timer.

SuperChip (S-CHIP) extends CHIP-8 with a 128×64 high-resolution mode, 16×16 sprites, scrolling, persistent flag registers, and a larger font. The SCHIP 1.1 interpreter by Erik Bryntse introduced several behavioral differences from the original CHIP-8. Select "SuperChip (Legacy)" for original HP-48 behavior or "SuperChip (Modern)" for updated quirks.

SCHIP Quirks & Compatibility: The SCHIP 1.1 interpreter introduced subtle bugs that became de facto standards due to its popularity:

• Shift instructions (8XY6/8XYE): Original CHIP-8 shifts VY into VX. SCHIP shifts VX in-place, ignoring VY. Programs wanting broad compatibility can use identical source and destination registers (e.g. VA <<= VA).
• Memory load/store (FX55/FX65): Original CHIP-8 increments I by the number of registers read or written. SCHIP leaves I unchanged. This prevents fast copy/draw/fill routines that rely on auto-incrementing I.
• Stack capacity: CHIP-8 provides 12 levels of subroutine nesting. SCHIP raises this to 16. No known SCHIP programs exceed the original 12-level limit.
• VF reset: In original CHIP-8, bitwise ops (8XY1, 8XY2, 8XY3) reset VF to 0. SCHIP does not.

This emulator follows original CHIP-8 behavior by default and provides "quirks modes" (Legacy/Modern) which selectively enable SCHIP-style behaviors, matching the approach used by the Octo toolchain.

SuperChip Instructions:

• 00FF — Enable 128×64 high resolution mode
• 00FE — Disable high res, return to 64×32
• 00CN — Scroll display down by N pixels (no wrap; v1.1 only)
• 00FB — Scroll display right by 4 pixels (no wrap; v1.1 only)
• 00FC — Scroll display left by 4 pixels (no wrap; v1.1 only)
• DXY0 — Draw a 16×16 sprite (32 bytes, row-wise: left byte then right byte per row)
• FX30 — Set I to large hex font character (8×10 pixels)
• FX75 — Store V0..VX in flag registers (X ≤ 7). Persisted to localStorage.
• FX85 — Load V0..VX from flag registers (X ≤ 7). Restored from localStorage on startup.
• 00FD — Exit the interpreter (halts emulation)

S-CHIP Flag Registers (RPL User Flags): These are 8 persistent 8-bit registers (R0-R7) separate from the V-registers. On the HP-48 calculator, these corresponded to 64 one-bit user flags (8×8-bit registers, so X must be 0–7). They survived power cycles and could even be shared between different programs. In this emulator, they are saved to localStorage for the same cross-session persistence. The opcodes FX75 (store) and FX85 (load) access these registers.

Keyboard mapping: 1234 / QWER / ASDF / ZXCV → CHIP-8 keys 123C / 456D / 789E / A0BF

Quirks by mode:

• CHIP-8: VF reset ✓, Memory increment (I += X+1) ✓, Display wait ✓, Shift VY→VX, Jump V0+NNN, Stack: 12 levels
• S-CHIP Legacy: No VF reset, No memory increment, Display wait ✓, Shift VX in-place, Jump VX+XNN, Stack: 16 levels
• S-CHIP Modern: No VF reset, No memory increment, No display wait, Shift VX in-place, Jump VX+XNN, Stack: 16 levels