Alex Finn

I really built a RAM bootloader for classic 68K CPU

Discussion created by Alex Finn on Mar 21, 2012
Latest reply on Apr 9, 2012 by Alex Finn

I am interested to design a small 68K system and I am working at it for some years.

There are several prototypes (wire based) as well one PCB design using the 68SEC000.


One prototype is in working order to a degree where it can store data into 128K SRAM, and read it back.

The MCU for instance could use it's hardware serial port for download.


Recently I received really large proto PCBs, and I am playing with the idea to connect the RAM bootloader to a PLCC 68000.

There is really no EPROM (or EPROMs) here.


However the software to load data to the RAM and to control the tristate is lengthy, somehow.


It's a old CPU I know. I have various types of them around, some Hitachi HC 68K with 2mm pitch, some old CERDIP 68k from Signetics, and PLCC from Motorola.


I even made another prototype with USB MCU, and 68008.


However I am not sure about developement software. There is one PC software Easy68k I think, it is not very stable on 64bit Windows.


What is your opinion, should I try to get one prototype running, or is it worth the efforts at all?


I have been reading through the users manual many times, at one point of time I was considering to write my own assembler in Visual Basic, but then stopped with that developement. Mainly for the reason there is no concrete need for it to have my own assembler.


I bought a CLPD board + JTAG programmer + downloaded the software, and I also have two GAL programmers now.


The PCB design for the 68SEC000 is not much bigger than 6cm x 6cm, including powerful MCU (as bootloader), and static RAM as well a small CPLD.


What I believe while reading the user manual I learned a lot about programming, and developed many other interesting circuits, so it was a good improvement for me. I don't really know if it makes sense to put too much effort into it.

Wire based prototypes require a lot of soldering, and more and more soldering. And then I sometimes saw the design was not good even before completion. I have 3 or 4 of these prototypes around, for the 68000, one 8086 board as well.

Unfortunately I did not draw schematics for them :smileyembarrassed:


If you have any input, feedback, opinion, please write it.

The bootloader even has 2 LED panels for address+data bus, detachable.