Cloning a 6502 Apple-1 in just 930 logic gates
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Cloning a 6502 Apple-1 in just 930 logic gates
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Re: Cloning a 6502 Apple-1 in just 930 logic gates
#2The C74-6502 is somewhat similar. A 6502 built using 74xx chips, that runs 20x faster than the 6502 (20Mhz vs 1MHz).
And correct enough that he drops it into both a VIC20, and a C64, and it works.
About ~130 74xx chips vs the Gigatron's 33, and SMT instead of through-hole.
Edit: A link to an old school web-ring of other homebrew (mostly) ttl logic CPUs: https://www.homebrewcpuring.org/ringhome.html
Re: Cloning a 6502 Apple-1 in just 930 logic gates
#3TL;DR: this is a very simple computer running an emulator. Cool project! (The approach is similar to the way many of FPGA applications are done these days.)
Re: Cloning a 6502 Apple-1 in just 930 logic gates
#4"It needs just 930 logic gates (packed into 33 standard 7400-series ICs) to create a computer that beat 'complex' 1980s home computers like the VIC-20 in terms of both CPU power and graphics."
Given that 7400 chips existed at the time, why did no contemporary microcomputer go this route? Would it just have been cost prohibitive?
Re: Cloning a 6502 Apple-1 in just 930 logic gates
#5"It needs just 930 logic gates (packed into 33 standard 7400-series ICs) to create a computer that beat 'complex' 1980s home computers like the VIC-20 in terms of both CPU power and graphics." Given that 7400 chips existed at the time, why did no contemporary microcomputer go this route? Would it just have been cost prohibitive?
There were commercial computers that did. The PDP-8, as one example (not 74xx, but similar).
Edit: The Xerox Alto CPU was built with 74181 chips.
Cost, power consumption, space, etc, are all disadvantages. I assume the Gigatron is using modern 74HCxx CMOS chips, which consume less power than the original 74xx TTL chips.
Re: Cloning a 6502 Apple-1 in just 930 logic gates
#6"It needs just 930 logic gates (packed into 33 standard 7400-series ICs) to create a computer that beat 'complex' 1980s home computers like the VIC-20 in terms of both CPU power and graphics." Given that 7400 chips existed at the time, why did no contemporary microcomputer go this route? Would it just have been cost prohibitive?
There were commercial computers that did. The PDP-8, as one example (not 74xx, but similar). Edit: The Xerox Alto CPU was built with 74181 chips. Cost, power consumption, space, etc, are all disadvantages. I assume the Gigatron is using modern 74HCxx CMOS chips, which consume less power than the original 74xx TTL chips.
Yes HC didn't exist and 4000 CMOS was slow. Plus the pcb, assembly and test cost for 40 DIP packages is significant.
Re: Cloning a 6502 Apple-1 in just 930 logic gates
#7"It needs just 930 logic gates (packed into 33 standard 7400-series ICs) to create a computer that beat 'complex' 1980s home computers like the VIC-20 in terms of both CPU power and graphics." Given that 7400 chips existed at the time, why did no contemporary microcomputer go this route? Would it just have been cost prohibitive?
The short answer is that computers with CPUs made from 7400 series TTL existed, but they weren't "micro".
Re: Cloning a 6502 Apple-1 in just 930 logic gates
#8I wonder how big the difference is between current logic gate performance vs. what we have available when the 6502 was 'new'.
Re: Cloning a 6502 Apple-1 in just 930 logic gates
#9I wonder how big the difference is between current logic gate performance vs. what we have available when the 6502 was 'new'.
Not a lot really, as far as the 74xx series goes. 10ns gate delay for the original 74xx TTL chips, vs 6ns gate delay for the current CMOS 74HCxx chips. The reduced power consumption is a bigger benefit.
Re: Cloning a 6502 Apple-1 in just 930 logic gates
#10TL;DR: this is a very simple computer running an emulator. Cool project! (The approach is similar to the way many of FPGA applications are done these days.)
It’s worth mentioning how simple the computer is. While the Gigatron is an 8-bit computer running at ~8 MHz (and probably more powerful than an 8086), it only has... seventeen instructions (with a few encodings for different operands). The instruction set is so limited, they created Gigatron Control Language (GCL) to allow you to write in a slightly higher level assembly.
So getting an emulator running is quite an achievement.