Posted May 19, 2007 by Mike from 8-Bit Domain:

I have been toying with the idea for several months of building a multi-
platform game development system.  I was mainly interested in consoles which 
have a true expansion interface like the Bally, Colecovision and Sega Master 
System, etc.  By true expansion interface I mean most if not all address, data 
and control signals.  These three consoles also have a common processor, the Z-
80 which I have worked with since the eighties.  I wanted something more that 
just a simple multicart with a download port.  So I designed this platform with 
its own processor and shared memory interface to the target console.  This 
allows me to take control of the target address/data bus utilizing BUSREQ and 
BUSAK of the Z-80.  Also I have a large expandable multibanked flash capability 
using the two 40 pin module sockets.  The platform having its own processor 
also means that I can diagnose and repair defective consoles (assuming that at 
least the Z-80 works).  The processor I use is the Atmel Mega128 with the 
Bascom AVR compiler.  It does not have to be code compatible with the target 
since the target console is basically shared memory and IO.  I can now write 
test routines for any memory or I/O device.  The Bally may be more difficult 
because of the custom video chips.  This Bascom AVR compiler source code would 
be open source and available to all to encourage a large database of software.  

     Check out the schematic, and read the complete discussion that followed Mike's posting.

A schematic in PDF of the Classic Console Development Platform that is in development by 8-Bit Domain. You can read more about it in this collection of postings to the Bally Alley Yahoo message group here.