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by mindcrime 3415 days ago
I love this. I started on a project to do a homebrew Z80 machine late last year as well. I haven't made much progress yet, but I'm really champing at the bit (no pun intended) to get this going. Reading stories like this is really motivational! And it's always good to learn from those who went before...
1 comments
XtalJ 3414 days ago
It is a really fun project to do, so I think you should continue :-) I'm going to add more documentation on the website, like timing diagrams etc. that may be useful for other people building a Z80 computer.
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mindcrime 3414 days ago
It is a really fun project to do, so I think you should continue :-)

Oh I will. Things just got bogged down over the holidays and everything late last year. My next step is to get everything setup so I can program an EEPROM with my Arduino so I'll have a way to load a program to bootstrap the system. I'm intentionally doing things the hard way though, to maximize my learning. For example, I'm using an Arduino Uno which doesn't have enough digital output pins to represent both the address bus and the data bus for the EEPROM. So instead of just grabbing a Mega out of the parts box, I am using SIPO shift registers to setup a serial -> parallel bus so I can program the EEPROM with fewer wires from the Arduino. No, it isn't efficient, but it'll teach me to use shift registers.

One of my other "next steps" is to just breadboard that Z80 "test circuit" and see if I can get some LED's to blink. I have to get the clock stuff figured out as well...

Like you said, it's a lot of fun. :-)

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XtalJ 3414 days ago
Sound like you have the right mindset ;-) The most boring part of the project was routing of all the bus lines in KiCad, but I knew that if a kept on working, the reward would be big :-)

I was actually planning to do a ROM emulator with a PIC MCU at first, but ended up using a regular EPROM, SIO/UART and a bootloader to load programs via RS232. When I had a stable program, I burned it to the ROM and continued. This is because when I got started with the "test circuit" I didn't want to go back to the PIC :-D

I'm currently developing my ROM monitor so that I can get CP/M running :-)

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