The Zilog Z80 has turned 50 • Hacker News Board

Re: The Zilog Z80 has turned 50

#71

Post by Zardoz84 » Sat, Jul 18, 2026, 7:23 AM UTC

II2II wrote: post #26

blauditore wrote: post #6

Earlier quoted context omitted.

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 selling waaay outdated hardware at horrendous prices.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on bit about horrible prices, the TI calculators are well suited to their intended task[1] so I will object to the outdated hardware part.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, fro…

I found a funny irony that in the country of free market, a calculator model was enforced nation wide in the schools. Here, in Spain, the teacher would only ask to the kids to get a calculator. They never ask for a concrete model or brand. Perhaps, they will only go ask to not get a programmeble calculator.

I agree that you not need to have more powerful calculator. A cheap Casio or HP calculator it's enough for the 99% of time. I keep using my old Casio from my formative years. It's in an interesting calc. Powerful enough to write formulas and complex calculations, but can't store formulas or programs. Just in the nice spot that allowed it to be used in exams.

Re: The Zilog Z80 has turned 50

#72

Post by timonoko » Sat, Jul 18, 2026, 7:38 AM UTC

Annoying part of 8080 was that the command set had holes in it and mystery restrictions. Which were hard to remember. And 12 undefined opcodes. Z80 solved all that.

However, you had to be a programmer Anno Dominii 1975 to fully understand what heavenly Joy and Jubilation Z80 was.

Re: The Zilog Z80 has turned 50

#73

Post by djmips » Sat, Jul 18, 2026, 7:50 AM UTC

mrandish wrote: post #57

ozhero wrote: post #7

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

I started 3 years later than you on a 4K Radio Shack computer running a 6809 8-bit CPU. I can still remember quite a few opcodes and a few months ago helped some on retrocomputing.stackexchange.com find a rather tricky 6809 assembly language bug without looking anything up. It's weird how stuff sticks around in our heads, since I haven't written any 6809 code in more than 40 years. Despite being entirely self-taught…

It feels a bit like a first language. That's the one that really sticks with you.

Re: The Zilog Z80 has turned 50

#74

Post by djmips » Sat, Jul 18, 2026, 7:51 AM UTC

adrian_b wrote: post #62

tasty_freeze wrote: post #27

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.

Making the parity flag not perfectly compatible was a wise choice. In legacy programs the parity flag was seldom tested and practically never after the instructions where in Z80 it behaved differently. This allowed the repurposing of the parity flag as an overflow flag, which was an extremely useful extension of Z80. The instruction sets of Datapoint 2200, Intel 8008 and Intel 8080 share with that of RISC-V the disti…

RISC-V has no overflow flag? That's fascinating. I'll have to dig into that!

Re: The Zilog Z80 has turned 50

#75

Post by djmips » Sat, Jul 18, 2026, 7:58 AM UTC

whartung wrote: post #9

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 tha…

Are you sure about that anecdote around the GBA? It would make more sense that they used the Sharp SM83 core - which is pretty far from a Z80 considering it's missing IX, IY and the entire alternate register set. It certainly does have some Z80 instructions and even some SM83 specific instructions. On the dial between 8080 and Z80 it feels closer to 8080 to me.

Re: The Zilog Z80 has turned 50

#76

Post by djmips » Sat, Jul 18, 2026, 7:59 AM UTC

jdw64 wrote: post #20

Back in the day, I studied Z80 assembly to write something about Pokémon red. I didn't realize it was this old

Sharp SM83 assembly. ;-)

Re: The Zilog Z80 has turned 50

#77

Post by userbinator » Sat, Jul 18, 2026, 8:08 AM UTC

Next to the TI calculators already mentioned by someone else, I think what might be the largest use of a Z80 core in a consumer product happened approximately 2 decades ago: https://en.wikipedia.org/wiki/S1_MP3_player

There was an active modding scene around them, and even some attempts at creating a replacement firmware, but unfortunately most of that seems to have disappeared.

Re: The Zilog Z80 has turned 50

#78

Post by nickdothutton » Sat, Jul 18, 2026, 8:09 AM UTC

I started out on Z80 when HLL compilers were expensive for me and the shareware alternatives weren’t so accessible as open source is today. Everyone should do at least a little assembler to gain an appreciation of what they are asking the machine to do, and the Z80 was simple enough to reason about.

Re: The Zilog Z80 has turned 50

#79

Post by timonoko » Sat, Jul 18, 2026, 8:13 AM UTC

timonoko wrote: post #72

Annoying part of 8080 was that the command set had holes in it and mystery restrictions. Which were hard to remember. And 12 undefined opcodes. Z80 solved all that. However, you had to be a programmer Anno Dominii 1975 to fully understand what heavenly Joy and Jubilation Z80 was.

And yes. There was 8080-assembler in PDP-11, but it was just regular PDP assembler with extra macroes. It did not know those forbidden commands and thus produced undefined opcodes with random and entertaining results.

Re: The Zilog Z80 has turned 50

#80

Post by bonzini » Sat, Jul 18, 2026, 8:32 AM UTC

djmips wrote: post #74

adrian_b wrote: post #62

Earlier quoted context omitted.

Making the parity flag not perfectly compatible was a wise choice. In legacy programs the parity flag was seldom tested and practically never after the instructions where in Z80 it behaved differently. This allowed the repurposing of the parity flag as an overflow flag, which was an extremely useful extension of Z80. The instruction sets of Datapoint 2200, Intel 8008 and Intel 8080 share with that of RISC-V the disti…

RISC-V has no overflow flag? That's fascinating. I'll have to dig into that!

It doesn't have a carry flag either. Multiprecision integer operations absolutely suck in RISC-V, you need three operations (SLT and two adds, with an awful dependency chain too) to do an add with carry, and op fusion can only do so much. At least add an instruction that computes the carry out, like "Rd = Cout(Rs1 + Rs2)" and the similar one for overflow...

https://gmplib.org/list-archives/gmp-devel/2021-September/00...