I couldn’t help but notice that the circuit layout looks like a uniform gate array rather something resembling a custom layout you usually see in die photos.
Zilog Z80 CPU – Modern, free and open source silicon clone
11–20 of 75 posts
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#12Z80 was the CPU of the ZX Spectrum. Oh the memories... https://en.wikipedia.org/wiki/ZX_Spectrum
So many good machines: the Amstrad CPC range, a whole slew of Sega consoles, the early MSX stuff and of course the Tatung Einstein. 3 inch disk machines of the world unite!
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#13What Tiny Tapeout is doing is amazing. Who would have thought that makers and students could have their own chip design made real for so little money? The tools look amazing as well. You'll won't design the next Intel CPU on that 130nm process but to think that the Z80 will fit on 0.064 mm2 is just amazing. It's great that there will still be an alternative to the official chip now that it won't be manufactured any m…
130nm process puts them at roughly Pentium III era. Not bad!
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#14Z80 was the CPU of the ZX Spectrum. Oh the memories... https://en.wikipedia.org/wiki/ZX_Spectrum
So many good machines: the Amstrad CPC range, a whole slew of Sega consoles, the early MSX stuff and of course the Tatung Einstein. 3 inch disk machines of the world unite!
Not to mention the world of CP/M business machines which was surprisingly large in the UK well into the late 80s, again thanks to Amstrad: https://en.wikipedia.org/wiki/Amstrad_PCW
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#15I had heard about Z80’s 4-bit ALU (2x for 8-bit math). Is this considered a major bottleneck? Were there later extensions that added higher bit integer math?
I’m curious whether an open source version of the chip will enable new features and variants.
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#16For those wondering, the 6502 and various derivatives are still being manufactured, by one of its original creators [0] - so I'd guess an equivalent development in the world of the Z80's nemesis is unlikely anytime soon. [0] https://www.westerndesigncenter.com/wdc/chips.php
And eZ80 (binary compatible, but not pin-compatible with Z80) is still being manufactured by Zilog.
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#17I had heard about Z80’s 4-bit ALU (2x for 8-bit math). Is this considered a major bottleneck? Were there later extensions that added higher bit integer math? I’m curious whether an open source version of the chip will enable new features and variants.
> Is this considered a major bottleneck?
No, because an ALU instructions with a register as source is already running as fast as possible (at 4 clock cycles, which is the duration of an opcode fetch 'machine cycle'). Or from a different perspective: an 8-bit ALU wouldn't have made math instructions faster, but would have cost twice as many transistors.
The 4-bit ALU is just an internal implementation detail that isn't visible to the outside (except maybe through the existence of the half-carry flag which indicated a carry from the lower into the higher nibble).
And if you want a CPU replacement that plugs directly into old home computers, the CPU needs to have the original instruction timing, otherwise software that depends on 'cycle counting' won't work (probably less of an issue on the ZX Spectrum though because the Speccy didn't have a programmable video hardware like for instance the Amstrad CPC).
The eZ80 is a modernised and more efficient design, with (among other things) a wider ALU: https://en.wikipedia.org/wiki/Zilog_eZ80. Not an option for keeping old home computers alive though, for this you'd want an exact Z80 clone with the original timings and undocumented behaviour.
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#18For those wondering, the 6502 and various derivatives are still being manufactured, by one of its original creators [0] - so I'd guess an equivalent development in the world of the Z80's nemesis is unlikely anytime soon. [0] https://www.westerndesigncenter.com/wdc/chips.php
65*C*02, which might fail if your 6502 code depends on illegal opcodes or incidental memory access or BCD math cycle timing or BCD math flags or perhaps decimal mode being set in an interrupt routine.
The 65C02 came out in 1983, so I think we've had plenty of time to document and workaround these issues!
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#19For those wondering, the 6502 and various derivatives are still being manufactured, by one of its original creators [0] - so I'd guess an equivalent development in the world of the Z80's nemesis is unlikely anytime soon. [0] https://www.westerndesigncenter.com/wdc/chips.php
Interestingly the classic z80 was end of lifed just two weeks ago.
https://hackaday.com/2024/04/19/end-of-life-for-z80-cpu-and-...
Re: Zilog Z80 CPU – Modern, free and open source silicon clone
#20Z80 was the CPU of the ZX Spectrum. Oh the memories... https://en.wikipedia.org/wiki/ZX_Spectrum
So many good machines: the Amstrad CPC range, a whole slew of Sega consoles, the early MSX stuff and of course the Tatung Einstein. 3 inch disk machines of the world unite!
All 8-bit computers manufactured in East Germany too (via the reverse enginered Z80 clone U880). For instance the KC85/2..4:
https://floooh.github.io/virtualkc/p010_kc85.html
An "Adrian's Digital Basement" episode about the KC85/3: