This guide explains how to access the SH-4 SCI port on Sega Dreamcast and NAOMI systems for both UART/SPI communication modes. This is can be used for alternative SD card modding or debugging. In SPI-like mode, SCI can reach transfer speeds of up to 1.5 MB/s, which is x2 faster than mod using the SCIF port for bit-bang SPI.

Sega Dreamcast Motherboard

Solder wires directly to the following points on the Dreamcast motherboard:

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