Most of what I did back in 80's and early 90's was writing software for the hardware, I designed and built.
I worked on the 8031/8751, 8085, and the Z80. On one occasion, I faced a challenge to build a Private Automatic Branch Exchange (PABX). The prototype was 8-Subscribers by 2-External lines. I planned to leave the majority of the tasks to be executed by the software to minimize hardware. At that time I was not well acquainted with Object Oriented programming, and everything had to be written in assembly. I realized from the start, in order to reach my goal successfully, I had to separate procedures/functions from data. Each subscriber/Extension had its set of data and flags as a separate entity. I needed a processor with a fair amount of ROM and RAM space, in addition to flexible addressing modes, comfortable room of internal registers, and unlimited stack space. There was critical timing involved, since everything was running in real time. At that time and for that specific project, the logical choice was the Z80 CPU.
All I had at the time was a PC-XT Amstrad running DOS, a Z80 cross assembler, a terminal app and a general purpose editor with a multi window feature. The target hardware was running a simple boot-loader/monitor program I wrote my self ... and that's it.
In my opinion, it is not the Z80, 6502, ATMega, or PIC. True, you have to make a choice on what resources you need for any specific task. However, what really matters here is the ecosystem behind the hardware of choice and whether there is an active community supporting the cause. I am very astonished here to find people still interested in the Z80!
If this enthusiasm builds up further then I won’t be surprised to find companies starting to re-invest in the Z80 and its chip-sets.
Moreover, Instead of inserting inline assembly code on a compiler, one day the trend might be; inserting inline high level code of the language of your choice in an assembly program.
It shouldn't cost you too much to get a Z80 and some support chips. I'd recommend the Z84C00 CMOS variant if because it has less limitations and some extra features.
The standard NMOS Z8400 part can't have a static clock signal whereas the CMOS version does.
You can be silly and make a flashing LED from a Z80 CPU ,a NE555 or crystal oscillator and a few 4k7 resistors. This doesn't really teach you much except that the Z80's NOP instruction is %00 (Hex) and if you've got an oscilloscope you can observe that the NOP instruction actually does something and the lower 7 bits of the address bus contain both the instruction fetch address and refresh RAM address.
You can get programming tools for the Z80 for free. Zilog offers ZDS2 for the eZ80. This can be used with the Z80 with a few tiny caveats. It even has a simulator and debugger.
Alternatively you can use one of the many emulators.
I am very interested in the Z80/Z180. I've wanted to build a a machine and see how much i can get out of this chip for 2 years now but sadly i am financially limited and have yet to obtain components to begin. I do know it is a widely available chip.
