I started programming in 1978 (In Assembler) and wanted to know not only how the software worked but how the hardware worked.
Found a great kit using the Z80 and built it and spent many nights with a logic probe and oscilloscope learning digital eletronics. Also devoured the Z80 manual learning the instruction set.
I'm nearly 70 now but remember those days like they were yesterday.
It sounds like it may be right up your alley. Its a simplified digital logic simulator, you make basic circuits from NAND gates, and then build these into functional units in later levels, then further on you build an instruction decoder, and combine it with these functional units and before long you have a Turing complete architecture and you are writing your own assembly on it - Assembly language that you defined, from scratch. You'll find the need for new opcodes... so, you build them!
Challenging game for sure, but very, very rewarding.
As the proud owner of a ZX-81 I remember staring at the Z80 instruction reference at the end of the user's manual without the faintest clue of what any of that meant. It took me some while before I managed to wrap my head around how CPUs actually run programs (vs. the high level abstractions like BASIC or other languages).
Actually, BASIC’s flat structure helped me a lot in understanding Z80 assembly when I was 12. You see, memory addresses were line numbers, registers were variables, JP was GOTO, CALL was GOSUB. CP was IF, JP, Z was THEN GOTO, and LD was LET, and so forth.
Another proud ZX-81 owner, my first computer bought as kit. It made me the TI pioneer in my little city. So cool times, everything was complex and simple at the same time. I had a flight simulator in only 1Kb ram :D
That machine was my intro to computers too, and I was fascinated by “fast mode” blanking the screen and the interesting tradeoffs between hardware and software.
Z-80 was the processor for my introduction to programming in assembly language on a TRS-80 model I in early 1983. Bill Barden's assembly language books and Hardin Brothers' "The Next Step" column in 80 Micro magazine paved the way.
I wrote a quick post a while back about my Z-80 experiences here:
The article claims:
> The Z80 is fully binary compatible with the 8080 instruction set.
It wasn't in regards to the flag register. The parity flag behaved differently for some ops.
And of course it would be possible to write an 8080 program that used undefined ops that would execute in some random way (often just duplicating an existing instruction) while the Z80 repurposed that opcode for something new.
35 years ago I had to program a Z80 by "assembling" programs by hand and punching hexcodes into a board. This was made easier by writing an assembler for it. This was my way into tools which took me eventually to working on a major C++ compiler.
The Z80 was how I learned assembly programming in high school.[0] Was a bit of an unusual choice, but high school students still carry these funky Z80 (or eZ80 now with the color screens) devices every day, so being able to hack on it and have plausible deniability while in class felt great :)
No mention of the TI-84 calculator? Used by millions of American schoolchildren, programmable in BASIC, and runs on Z80 (B/W models)/eZ80 (color display models) to this day
Europe too :) When I was in high school, TI-84 Plus was the calculator the school told all of us to buy. And I see that stores in my country are still stocking them so I have to assume they are still being bought and used.
Many hours were spent by me and my friends making and showing off little programs in TI-BASIC on those calculators. None of us ever took it all the way to learning Z80 assembly however. I printed a whole manual about Z80 assembly programming for the TI-84 Plus and started reading it but never wrote a single line of assembly for it. Yet.
We had both depending on the school and sometimes even the teacher. fx-9750G and GII didn't support assembly programming... unless you used an undocumented procedure to flash them with unsupported firmware from a different calculator model...
Same here (actually had a voyage 200, but same same I guess). It's actually quite insulting that TI kept (and keeps?) selling waaay outdated hardware at horrendous prices. It's the SAP/Oracle business model applied to school hardware.
While I agree on bit about horrible prices, the TI calculators are well suited to their intended task[1] so I will object to the outdated hardware part. Stability is a good thing in the context of classrooms. Why should schools be spending money on replacement hardware, software, and textbooks when the curriculum itself is fundamentally unchanged?[2]
[1] Except the screens on the older models were truly horrible, from a brightness and contrast perspective.
[2] From my recollection, the calculators interfaced with hardware and software from other vendors. Then, of course, there was the vendor lock-in provided by textbook publishers.
> Same here (actually had a voyage 200, but same same I guess).
Not the same, actually! Unlike the TI-83/84 series, the TI-89, -92, and Voyage-200 all used a 68000 CPU, with a completely different (and much better) operating system.
There are plenty of open core alternatives that replicate the architecture and ISA. Many of these are cycle accurate. Some have been tape-out proven. Hobbyist retro-computing enthusiasts who wish to build a Z80 system still have options even once new old stock and recovered CPUs become scarce.
The heart of the mighty Australian Microbee. I still have the Rodney Zak’s book somewhere although I’ll admit doing anything fancy with assembler back then was a bit beyond me
This is the CPU that I first learned to code on, first in TI Basic (TI-8[1356] ftw) and then Z80 assembler. Crazy to think that the CPU was "old" when I started, and it's still doing good work in those calculators even 20+ years later.
First, my Father wanted to try to add some peripherals to the original TRS-80 Model 1. So, what he was interested in doing was asserting the BUSREQ pin to tell the Z80 to get ready so that he could have the bus, ideally waiting for the BUSACK signal to know when it was his.
Unfortunately, on the Model 1, when you assert the BUSREQ pin, it is tied directly to the tri-state buffers that handle the address and data bus. So, as soon as you make the request, the Z80 loses all access to its memory and data -- mid cycle. Which, you know, can be Bad. Radio Shack labels this pin TEST and uses it for internal testing. But it was definitely a bit of a disappointment to my Fathers efforts.
The second one is when I learned that the Game Boy Advance has a Z80 built into its chip. The designers drag and dropped a Z80 core (tweaked for GB) just so they could run legacy GB games on it. It just kind of bends your view of the computing world when something as significant as a Z80 can just be shoved into the corner of a die for "just in case" functionality.
That just means you have a more exciting design problem! Now you have to stop the clock and then assert TEST for probably a certain maximum number of cycles (dynamic logic) before enabling the clock...
I still remember clearly sitting down to play with the TRS-80 at the local Radio Shack in the 1970s
Unlike anything I had ever experienced, it was life changing, I would bike to the store every day after school
Family couldn't afford the computer but I bought all the books and would read them at home over and over and gawk at all the accessories in the catalogs
Then family surprised me with it as a birthday present with all the relatives paying for it, pretty sure I was the only person in town with one, even the school didn't get one for years
Didn't have any way to save programs, not even the cassette recorder which was too expensive, had to memorize them and retype every time I turned it on
Happy birthday! The Z80 was the first CPU I rode, more luxurious than the subsequent 6502 and 6510. I still have a TI calculator with a low-energy Z80.
The MOS 6502 was introduced at the WESCON tradeshow in September 1975 and sold for $25 quantity 1. They had a transparent vase full of them, 'proving' they did volume -- but those were all chips that failed post-manufacturing testing, except for the very top layer. Still...
Spoiler: the undocumented WZ registers are just microcode temporaries to hold large operands. For instance when reading a jump instruction, the jump destination can't be read directly into PC since that would mess up reading the second half of it, so it's read into WZ and then WZ is transferred to PC. This is invisible to the programmer.
One might say the instruction is really "jump to WZ", or JWZ, which, of course, refers to Jamie Zawinski (not really).
I started programming in 1978 (In Assembler) and wanted to know not only how the software worked but how the hardware worked.
Found a great kit using the Z80 and built it and spent many nights with a logic probe and oscilloscope learning digital eletronics. Also devoured the Z80 manual learning the instruction set.
I'm nearly 70 now but remember those days like they were yesterday.
Truly a magnificent CPU
May I suggest you check out the game "Turing Complete" https://turingcomplete.game/
It sounds like it may be right up your alley. Its a simplified digital logic simulator, you make basic circuits from NAND gates, and then build these into functional units in later levels, then further on you build an instruction decoder, and combine it with these functional units and before long you have a Turing complete architecture and you are writing your own assembly on it - Assembly language that you defined, from scratch. You'll find the need for new opcodes... so, you build them! Challenging game for sure, but very, very rewarding.
The game is still in early access, but very near a full release. They just put out a trailer: https://www.youtube.com/watch?v=goclUECM2ds
Same! Also built external peripherals for my ZX81.
As the proud owner of a ZX-81 I remember staring at the Z80 instruction reference at the end of the user's manual without the faintest clue of what any of that meant. It took me some while before I managed to wrap my head around how CPUs actually run programs (vs. the high level abstractions like BASIC or other languages).
Actually, BASIC’s flat structure helped me a lot in understanding Z80 assembly when I was 12. You see, memory addresses were line numbers, registers were variables, JP was GOTO, CALL was GOSUB. CP was IF, JP, Z was THEN GOTO, and LD was LET, and so forth.
Another proud ZX-81 owner, my first computer bought as kit. It made me the TI pioneer in my little city. So cool times, everything was complex and simple at the same time. I had a flight simulator in only 1Kb ram :D
That machine was my intro to computers too, and I was fascinated by “fast mode” blanking the screen and the interesting tradeoffs between hardware and software.
Z-80 was the processor for my introduction to programming in assembly language on a TRS-80 model I in early 1983. Bill Barden's assembly language books and Hardin Brothers' "The Next Step" column in 80 Micro magazine paved the way.
I wrote a quick post a while back about my Z-80 experiences here:
https://jimlawless.net/blog/posts/z-80/
The article claims: > The Z80 is fully binary compatible with the 8080 instruction set.
It wasn't in regards to the flag register. The parity flag behaved differently for some ops.
And of course it would be possible to write an 8080 program that used undefined ops that would execute in some random way (often just duplicating an existing instruction) while the Z80 repurposed that opcode for something new.
35 years ago I had to program a Z80 by "assembling" programs by hand and punching hexcodes into a board. This was made easier by writing an assembler for it. This was my way into tools which took me eventually to working on a major C++ compiler.
RE "....assembling programs by hand and punching hexcodes into a board......"
You translated you assembly language to machine language. ( Machine language is the only language a CPU can understand. )
The Z80 was how I learned assembly programming in high school.[0] Was a bit of an unusual choice, but high school students still carry these funky Z80 (or eZ80 now with the color screens) devices every day, so being able to hack on it and have plausible deniability while in class felt great :)
[0] https://github.com/siraben/zkeme80
No mention of the TI-84 calculator? Used by millions of American schoolchildren, programmable in BASIC, and runs on Z80 (B/W models)/eZ80 (color display models) to this day
> Used by millions of American schoolchildren
Europe too :) When I was in high school, TI-84 Plus was the calculator the school told all of us to buy. And I see that stores in my country are still stocking them so I have to assume they are still being bought and used.
Many hours were spent by me and my friends making and showing off little programs in TI-BASIC on those calculators. None of us ever took it all the way to learning Z80 assembly however. I printed a whole manual about Z80 assembly programming for the TI-84 Plus and started reading it but never wrote a single line of assembly for it. Yet.
It depends on the country I guess. In Spain I never saw a person using Texas Instruments calculators. Casio and HP are way more popular.
We had both depending on the school and sometimes even the teacher. fx-9750G and GII didn't support assembly programming... unless you used an undocumented procedure to flash them with unsupported firmware from a different calculator model...
Same here (actually had a voyage 200, but same same I guess). It's actually quite insulting that TI kept (and keeps?) selling waaay outdated hardware at horrendous prices. It's the SAP/Oracle business model applied to school hardware.
While I agree on bit about horrible prices, the TI calculators are well suited to their intended task[1] so I will object to the outdated hardware part. Stability is a good thing in the context of classrooms. Why should schools be spending money on replacement hardware, software, and textbooks when the curriculum itself is fundamentally unchanged?[2]
[1] Except the screens on the older models were truly horrible, from a brightness and contrast perspective.
[2] From my recollection, the calculators interfaced with hardware and software from other vendors. Then, of course, there was the vendor lock-in provided by textbook publishers.
> Same here (actually had a voyage 200, but same same I guess).
Not the same, actually! Unlike the TI-83/84 series, the TI-89, -92, and Voyage-200 all used a 68000 CPU, with a completely different (and much better) operating system.
I wrote a web-based emulator for the Voyage-200 a few years ago: https://woofle.net/v200/
TI-83 for me. We didn't have that advanced technology.
TI-83 was built on Z80 as well. I remember hand-assembling a program for it with pen and paper, something I did earlier with the Sinclairs.
The Z80 stopped being manufactured last year unfortunately
There are plenty of open core alternatives that replicate the architecture and ISA. Many of these are cycle accurate. Some have been tape-out proven. Hobbyist retro-computing enthusiasts who wish to build a Z80 system still have options even once new old stock and recovered CPUs become scarce.
There are clones, and updated packages these days like the EZ80, but they're not the same and they don't have the easy-to-use DIL form-factor.
Still I've always loved the z80, since my first computer the ZX Spectrum. Even now I play with z80 assembly now and again (mostly for CP/M retro-use).
My first computer was a soviet clone of a ZX Spectrum, which started it all almost 40 years ago...
There is a drop in compatible FOSS clone of Z80 https://github.com/rejunity/z80-open-silicon
The heart of the mighty Australian Microbee. I still have the Rodney Zak’s book somewhere although I’ll admit doing anything fancy with assembler back then was a bit beyond me
What a milestone. Still my favorite processor, and I have about 10 here at home in various yet to be finished projects (of course).
This is the CPU that I first learned to code on, first in TI Basic (TI-8[1356] ftw) and then Z80 assembler. Crazy to think that the CPU was "old" when I started, and it's still doing good work in those calculators even 20+ years later.
Two of my favorite Z80 anecdotes.
First, my Father wanted to try to add some peripherals to the original TRS-80 Model 1. So, what he was interested in doing was asserting the BUSREQ pin to tell the Z80 to get ready so that he could have the bus, ideally waiting for the BUSACK signal to know when it was his.
Unfortunately, on the Model 1, when you assert the BUSREQ pin, it is tied directly to the tri-state buffers that handle the address and data bus. So, as soon as you make the request, the Z80 loses all access to its memory and data -- mid cycle. Which, you know, can be Bad. Radio Shack labels this pin TEST and uses it for internal testing. But it was definitely a bit of a disappointment to my Fathers efforts.
The second one is when I learned that the Game Boy Advance has a Z80 built into its chip. The designers drag and dropped a Z80 core (tweaked for GB) just so they could run legacy GB games on it. It just kind of bends your view of the computing world when something as significant as a Z80 can just be shoved into the corner of a die for "just in case" functionality.
Just shows how far we had come at the time.
That just means you have a more exciting design problem! Now you have to stop the clock and then assert TEST for probably a certain maximum number of cycles (dynamic logic) before enabling the clock...
My son programmed a Z80-based instruction set into a Juno probe sensor. Still kicking.
Off topic: nice, retro website look!
I still remember clearly sitting down to play with the TRS-80 at the local Radio Shack in the 1970s
Unlike anything I had ever experienced, it was life changing, I would bike to the store every day after school
Family couldn't afford the computer but I bought all the books and would read them at home over and over and gawk at all the accessories in the catalogs
Then family surprised me with it as a birthday present with all the relatives paying for it, pretty sure I was the only person in town with one, even the school didn't get one for years
Didn't have any way to save programs, not even the cassette recorder which was too expensive, had to memorize them and retype every time I turned it on
Happy birthday! The Z80 was the first CPU I rode, more luxurious than the subsequent 6502 and 6510. I still have a TI calculator with a low-energy Z80.
Cheers to Rodnay Zaks for "Programming the Z80"!
https://archive.org/details/Programming_the_Z-80_2nd_Edition... is where I learned about the "W" and "Z" registers -- if you don't know what they do, I won't spoil your fun reading Zaks! See also http://www.z80.info/zip/z80-documented.pdf
The MOS 6502 was introduced at the WESCON tradeshow in September 1975 and sold for $25 quantity 1. They had a transparent vase full of them, 'proving' they did volume -- but those were all chips that failed post-manufacturing testing, except for the very top layer. Still...
Spoiler: the undocumented WZ registers are just microcode temporaries to hold large operands. For instance when reading a jump instruction, the jump destination can't be read directly into PC since that would mess up reading the second half of it, so it's read into WZ and then WZ is transferred to PC. This is invisible to the programmer.
One might say the instruction is really "jump to WZ", or JWZ, which, of course, refers to Jamie Zawinski (not really).
Back in the day, I studied Z80 assembly to write something about Pokémon red. I didn't realize it was this old