Authoritative spec docs cite Intel MCS-4 (Feb 1973) and MCS-40 (Nov 1974)
manuals page-by-page. Reference-implementations doc surveys four
permissively-licensed open-source emulators (markablov/i40xx,
Kostu96/K4004, lpg2709/emulator-Intel-4004, alshapton/Pyntel4004) for
cross-validation, explicitly excluding GPL sources (MAME mcs40,
carlini/intel-4004-in-4004-bytes-of-c).
Critical findings:
- 4040 interrupt vector is fixed at PC=0x003 (no vector table).
- New 4040 instructions all live at OPR=0000, OPA=0x01..0x0E.
- 4004 DAA (opcode 0xFB) is single-nibble, very different from 8080.
- 4040 STP/STPA/INTA pin names per datasheet (not STOP/STOPACK).
- R16..R23 are not directly named — they're Bank-1 R0..R7 via SB0/SB1.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
David Montero