The Dreamcast uses the SD card connected directly to
the serial port,
 it would take some circuitry to connect a CF into that port. 
Um, Dreamcast VMUs are more than just SD cards; they've got an 8-bit
CPU and a small 1bpp display in there too.  And the SH's serial port is
brought out to a connector on the back panel....
Unless you mean something other than the Sega gaming console?
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