I can answer your question, which is quite complex and involves both
CPU
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
SHmedia.
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
www.renesas.com) 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
chips.
Sorry that we do not have any better solution for you.
Best regards
Mark Jones
Business Development
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