Siemens PC 100 Assembly Manual Reveals Undocumented 6502 Opcodes
2025-05-09
A 1980 Siemens PC 100 assembly manual surprisingly documents "illegal" opcodes for the 6502 processor. The PC 100, based on the Rockwell AIM-65, features extra instructions labeled "Sonderbefehle" (special instructions), including AAX, DCM, LAX, and ISB, offering potential performance gains for programmers. While not officially supported and subject to change, these undocumented opcodes reveal a deeper understanding of the 6502 by Siemens engineers, adding a fascinating layer to retrocomputing history and highlighting the creative exploration of hardware and software capabilities at the time.
Hardware
Siemens