Authoritative spec from Intel iAPX 86,88 User's Manual (1979) +
embedded 8282/8283 datasheet in Appendix B. Cross-validation against
three permissively-licensed open-source emulators:
- 8086tiny (MIT, Adrian Cable, ~600 LOC)
- MartyPC (MIT, dbalsom, hardware-validated, 99.9997% on 8088 V2 tests)
- YJDoc2/8086-Emulator (Apache+MIT, partial)
Excluded GPL refs: Fake86, DOSBox, MAME, QEMU.
Critical findings for clean-room implementation:
- 40-pin DIP min-mode pinout with AD0..AD15 multiplexed (low addr in
T1, data in T2..T4) and A16..A19/S3..S6 multiplexed.
- Reset state: CS=0xFFFF, IP=0, all other segs=0. Physical first
fetch at 0xFFFF0.
- ALE pulses high in T1, falls at end of T1 — external 8282 latches
on falling edge to demux.
- ModR/M decode: 16-bit effective-addr table from the manual.
- DAA differs from 8080 only in the carry-treatment around BCD
borrow; AAA/AAS/AAM/AAD specific to 8086.
- MUL/DIV: OF and CF defined; SF/ZF/AF/PF undefined per Intel.
- Undocumented: POP CS (0x0F) and SALC (0xD6) — original 8086 only,
removed in 80186+.
PDFs (62 MB iAPX manual, 215 KB 8282 datasheet) saved under pdfs/.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
David Montero