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Z80 or similar bare bone computer.

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I am interested in building a small computer and had previously opted to build a very minimal computer out of discrete components (think 4- bit). Due to cost constraints and my skill level in electronics I don't think I can do this at the current time. So, I have opted to try building a small computer with a pre-built retro cpu.

First, my two goals:
<>I do not want a computer with extra capabilities like serial output or the ability to drive a display. I want a "bare bone" computer. This entails a dip switch input and led indicating output. I would also like the option to switch to some sort of latching system for the inputs and outputs so my computer can control and be controlled by peripherals as my skill level increases.

<>Ideally I would like to have as few chips as possible.

I was initially planning to use a Z80 as the cpu because wikipedia says it had the need for less supporting ic's than its predecessors. Also, there is a lot of documentation out there on the cpu. Yo may be asking why I am asking for advice then but the truth is because the Z80 computer building tutorials I have found all involve a screen and are more complex than I can manage. If there is another processor that is easier to work with, please tell me!

As best I can figure, for my basic computer I would need: the processor, a ram chip, a rom chip, 8 latches for the input and for the output (for an 8 bit processor), an 8 switch dip switch, a clock, and an 8 led display. Are there any other chips I am missing (buffers or the like)?

Also, how can a program be written to the cpu? My thoughts on this were that the very first address of the rom section would have instructions to read say bit 1 and bit 2 of the input.

It would keep doing this if both were low and when bit 1 goes high it triggers the cpu to jump to a section of rom which performs a loop where it reads the input->stores it in a certain memory address allocated to storing programs-> increments this memory address by 1->reads and stores the next input.

If it read a bit 2 initially it would jump to the memory address where program starts.

All in all this seems like a very bad way to program, what is the best way to program. I am farely certain that some startup program will need to be written to the first address of memory in the rom.

Thanks for your help.

you might want to play with microcontreollers first ? I've never played with "neat" processors as yes there is more than meets the eye in making a computer from scratch as you also have to look at how your going to have the software and hardware interact, we take this for granted in modern computers but the fundamentals of the x86 platform were laid down years ago and have no changed much since

My first thought was the old Talking Electronics TEC-1D computer:
Looks like you can still buy the kit, and there is plenty of documentation to go along with it.


this was my first idea in building a discreet components computer. just to share the thought, might be a good project for my students. one batch of them did this years ago ;)


--- Quote from: EEVblog on October 07, 2010, 06:58:14 am ---My first thought was the old Talking Electronics TEC-1D computer:

--- End quote ---

Great computers. I learned to program Z80s in hex with them, and still have mine gathering dust in the shed. 3E 00 D3 03 76. Talking Electronics also sold a stripped down version with just I/O and an EPROM (ie, without the keypad and LEDs) for use in embedded controllers. It'd be worth looking at the schematics for this one, as it was pretty minimalistic, but the TEC-1 wasn't a lot more complicated.


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