Design of a 68020-based SBC

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My interest in the 68000 family of MPUs stems from two things: it’s use in my all time favourite computer, the Amiga. And the fact that it’s generally considered a very clean design compared to its then main competition. Not that this is a high bar; anything prior to the 386 is dreadful and the later CPUs are not much… Read more »

Keyboard debouncing and designing a case

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One critical issue arises when attaching mechanical switches, as found in computer keyboards, to digital electronics: switch bounce. When switches are opened and closed, the connection across the switch contacts does not cleanly transition from its previous state to its new state. Instead the switch contacts will (literally) bounce between the old state and new state before finally, after a… Read more »

Switching to WordPress

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This is completely “off topic” but worthy of a post. You may have noticed that this blog has been moved off Google’s blogspot platform onto a blog running in WordPress. I’ve never been particularly happy with blogspot. It largely works, but… The big problem (by far) is the post editing control is just awful. Unspeakable bad, in fact. And I… Read more »

An analogue joystick and implementing an SPI controller

It’s been a while since my last post. The main reason being a house move. On the plus side this is good for my projects as I now have lots more room to work on them. On the negative side, at least as far as my hobbies are concerned I’ve, somewhat unexpectedly, found myself doing some work for my old company…. Read more »

Exploring C compilers for the 6809

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Ever since I fired up my first 6809-based computer, I have wondered about the possibility of running programs written in something other then assembly language on it. Not that I don’t love writing code in assembly. But for interests sake, and because it could be a different kind of fun, I’ve been curious about running code written in higher level… Read more »

Code reorganisation, debug monitor, IDE, MinixFS

I have restructured the source code tree for MAXI09OS. Source files are now grouped in directories, with a directory for drivers, another one for the core of the OS, etc. The assembly source files are no longer stuck in a single directory. The makefiles are, by necessity, a little more complex as a result. After toying with using make in… Read more »

More progress…. Lots of different areas

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Looking again at the VHDL for my interrupt router, I realised that adding a priority encoder was fairly simple: Instead of being the masked and active interrupt lines, ROUTED is now the number (bit position plus one) of the active line. 0 is used as a special case: no interrupt lines, which are exposed by the mask, are active. This… Read more »