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The Tiniest, Minimalist 68K

A project log for Melting the Balls off the DragonBall

Hand Soldering DragonBall 68EZ328 BGA

PlasmodePlasmode 01/20/2018 at 15:230 Comments

Motorola's 68328, aka DragonBall, was designed in late 1990's for handheld computer such as the Palm. It is an highly integrated processor with a 68EC000 core. Among the peripheral is a LCD controller which was why I bought some in the first place 5+ years ago. To my dismay, I realized I've purchased the BGA version that's too difficult to prototype, but the price is right so I kept them for my 68K CPU collection.

There is an interesting bootstrap feature on 68328 that supports serial communication with the processor and its peripherals without any external ROM/RAM. Only a dozen signals need to be connected to enable the bootstrap mode. Better yet, the software tool for interfacing in bootstrap mode is still available on the NXP website. So it is conceivable to hand wire a dozen wires to the tiny BGA and earn the bragging right of having power up the tiniest, minimalist 68K system, for what it's worth.

This is the schematic for enabling the bootstrap mode. All is needed is hookup a 32.768Khz crystal , ground nEMUBKT while resetting and talk to the serial port, that's it. The initial baud rate is 9600, but bbug.exe changes it to 19200, it can even be configure to 115200. bbug.exe is a DOS program with a few basic commands, display memory, modify memory, load program, and go. This is a screen shot of 16 bytes memory in 0xFFFFFF00 being displayed.

So there you have it, the tiniest, minimalist working 68K computer!

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