the Z80 outlived the company that made it, the company that bought that company, and will probably outlive whatever acquires the remains next
The Zilog Z80 has turned 50
61–70 of 131 posts
Re: The Zilog Z80 has turned 50
#62The 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 distinction of belonging to the extremely few ISAs where overflow is not detected by hardware.
Datapoint 2200 and its first successors had the excuse that they were extremely simple and cheap designs, which were never intended for general-purpose computing.
RISC-V has absolutely no excuse. The lack of overflow detection is its greatest mistake.
Re: The Zilog Z80 has turned 50
#6335 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.
During the eighties, there were a lot of people, including myself, who could read directly the hex codes of the Z80 instructions as easily as its symbolic assembly language.
That was very handy for reverse engineering programs like the Microsoft CP/M BASIC interpreter or FORTRAN compiler.
Re: The Zilog Z80 has turned 50
#64[dead]
Re: The Zilog Z80 has turned 50
#65[dead]
Re: The Zilog Z80 has turned 50
#66I had no idea about the Exxon connection to Zilog. That was wild.
Arguably, Exxon's plan to build a computing ecosystem rival to IBM's would have worked too, if the 16 bit successor of the Z80 would have maintained upward binary compatibility with Z80.
CP/M was an absolute beast in the era, with massive installed base and software support, employing 500 people in 1982. A CPU that could run unmodified Z80 software in a 64k segment would have allowed DRI to ship 16 bit CP/M with only basic tweaks and likely kill the market for the PC.
It was, famously, DRI dragging their feet on 8086 support that motivated the release of QDOS, which was then bought by Microsoft and relicensed at an immense markup to IBM as MS-DOS.
Re: The Zilog Z80 has turned 50
#67The 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.
But "undefined ops" are not part of the "8080 instruction set"; supporting those would be "binary compatible with the 8080 silicon". The parity flag is a breaker though; "binary compatible for code only relying on the 8080 instruction set, other than values of the parity flag".
By the same thinking that have the parent post The 80286 and 80386 aren't binary compatible with the 8086. Because they replaced undefined opcodes with new stuff.
Re: The Zilog Z80 has turned 50
#68No 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…
Not all of Europe, Portugal was all about Casio and HP.
Re: The Zilog Z80 has turned 50
#69Earlier quoted context omitted.
> 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…
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.
and nobody enforces a calculator model
Re: The Zilog Z80 has turned 50
#70Happy 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"!
Zaks is a name I remember fondly, but for me the starting point was "An Introduction to z80 machine code" by R.A & J.W Penfold.