This one became a three-part project:

  1. disassemble the Game Unit
  2. desolder the BIOS ROM
  3. dump the contents

The BIOS chip is labelled MPR-15768-T.

It is a mask ROM rather than an erasable 27C1024 EPROM, but I was able to read it using a 27C1024-compatible setup.

A 27C1024-class device stores 1 megabit as 64K x 16 bits, which works out to 128 KiB.

That is also the size of the BIOS image I dumped.

At the time, I believed this was the first public dump of the Aiwa BIOS.

I cannot independently prove that priority claim now, so I would rather preserve it as what I understood in January 2013 than turn it into a definite modern claim.

What I can establish is that MPR-15768-T is now preserved and catalogued as a 128 KiB Aiwa Mega-CD BIOS image, with CRC32 8052c7a0.

That makes this little exercise rather more interesting than simply practising with the programmer.

I later came back to this same area of the Game Unit to install a BIOS socket, repair damaged traces and burn replacement EPROMs.

For now, though, the important bit is done:

BIOS preserved.

More details from the original investigation can be found in the archived ASSEMblergames thread.

Sources