Johnny's homebuilt 8080 CPU corner (and other stuff, maybe)
While trying out stuff I stumbled over one so simple problem that I had to make a new XBUS board to solve it. Overkill, maybe, but as usual, fun.
While this became an issue where when I tried to make a simple interface to an 16x2 LCD module using the XBUS parallel board.
The initializing part of the LCD module requires some waiting times between commands and that made me wonder - If I write a software timing loop, for the 8080, then that timing loop will be different depending on the currect clock speed of the 8080. Not god.
So I set out to solve that problem by constructing a timer in hardware, with its own 10 MHz Xtal oscillator, that could be set to count out a sertain number of clock ticks to eat up time. In the meanwhile the timer would use the /WAIT signal to temporaily halt the 8080 until the time is up.
This timer has never been tested, but as usual, it looks great on paper!
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Note: The ring is chartered for projects that include a home-built CPU. It can emulate a commercial part, that′s OK.
But actually using that commercial CPU doesn′t rate. Likewise, the project must have been at least partially built: pure paper designs don′t rate either.
It can be built using any technology you like, from relays to FPGAs.