The Microsoft SoftCard for the Apple II: Getting two processors to share memory
6 months ago
- #Apple II
- #Microsoft
- #CP/M
- The Microsoft Z-80 SoftCard was a plug-in expansion card for the Apple II, enabling CP/M software execution.
- It was Microsoft’s first hardware product and a major revenue source in 1980.
- The card included a Zilog Z80 processor, compatible with CP/M's 8080 requirements.
- The 6502 and Z80 processors coexisted by using DMA signaling and the Z80’s REFRESH line to manage memory access.
- Memory remapping was used to resolve conflicts between the Z80 and 6502 memory usage.
- The SoftCard manual provided detailed instructions on writing code, including calling 6502 subroutines from Z80.
- The SoftCard facilitated business software development on the Apple II, leveraging tools like WordStar and Pascal MT+.