Introduction (1st January 2005)

Inspired by cgfm's work on interfacing Sega pcb's to PC's using a USB link I decided to try something similar but more general. The easiest way I could think of was to overlay some kind of read port into the rom space of a game - that way you get access to the address & data bus but without needing to know any details such as custom cpu pinouts. It also works with any type of cpu (68000, ARM, Z80, etc). I briefly investigated a USB link to PC but decided on parallel port as it's cheaper and simpler. Some TTL logic is used to interface the parallel port with the rom socket. With a link in place all that is needed is software on both PC and the target platform to communicate over the link.

Why?

With an interactive link from PC onto a target pcb it is easy to probe protection devices so that they can be emulated. It is also easy to figure out specific graphics effects or unknown registers and test timing.

Software

The target software consists of a 'kernel' for each target CPU type and a 'driver' for each target platform. So, the game Rohga would use the 68000 kernel and a specific driver to implement the game specific parts. A game like Fighter's History would use the ARM kernel and specific driver.

As well as allowing you to read/write in the address space of the target CPU you can put together script files of multiple commands, or upload binary data. By combining upload & execute you can run programs on the target cpu to test things like timing which are hard to do interactively.

Download

Software and hardware schematic will be avaliable for download after I tidy everything up a little.

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