Z80 Assembly 46: File I/O and SD Card Interfacing (Mass Storage)
The Challenge of Mass Storage Traditional Z80 systems used slow tape drives, but modern retro systems often use SD cards or CompactFlash for fast, reliable storage. The Z80 must communicate with these devices using a low-level protocol, typically SPI (Serial Peripheral Interface). The SPI Protocol (Simplified) SPI is a synchronous serial protocol that sends data one bit at a time over several dedicated lines controlled by I/O ports: Line Direction Purpose CLK Output The Clock signal (controls timing). MOSI Output Master Out, Slave In (Data sent from Z80 to SD card). MISO Input Master In, Slave Out (Data received by Z80 from SD card). CS Output Chip Select (Activates the specific SD card). Bit-Banging the SPI Signal Since the Z80 doesn’t have a native SPI controller, we must bit-bang the protocol entirely in software using fast I/O port writes and reads. ...