I can answer your question, which is quite complex and involves both
architecture and specific device information.
1. The SH-4 is a 32-bit CPU with an instruction set branded as
SHcompact. The SH-5 is a 64-bit CPU that supports the SHcompact
instruction set and adds a new multimedia instruction set called
This means that binaries written for SH-4 would run on SH-5. However in
the Dreamcast there are many peripherals and system components and
changing CPU is not really a practical option unless you have access to
the all the source code written by Sega. You could contact Sega but I
doubt they will give out this material.
2. Pin compatibility
The Sega Dreamcast was built with the SH-4 CPU and a set of peripherals
e.g. memory interface, UART etc. The actual device was manufactured by
Hitachi Semiconductor (now called Renesas Technology, see
) but it is not for sale any more.
There is no version of the SH-5 that is pin compatible with the SH-4
device used in the Dreamcast so it is not possible to swap out the
Sorry that we do not have any better solution for you.