Emulating the 6502 CPU in C++ (2021) [video] | Hacker News Reader

Emulating the 6502 CPU in C++ (2021) [video]

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61 pointsmariuz14 comments

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6502 is the greatest of all time. Last I checked they were making them out of plastic

6502 is awesome, but Z80 had more registers, the ability to combine pairs of them into 16 bit index registers, shadow registers, a plethora of bit instructions, and repeating string instructions.

Clock for clock 6502 was faster than Z80. I think 6502 was also cheaper. Of course Z80 did run at higher clock speeds.

6502 got practically 254 (6510) or 256 "registers" with zero page addressing.

Yes, clock for clock on the single-register subset of instructions you could directly compare. But A) z80s usually ran 4-8x faster, B) they had more registers which closed the gap on more complex instructions and C) they didn't have a special Zero Page that had to be juggled for maximal efficiency.

The 6502 was great for it's economy and simplicity. But it wasn't some architectural marvel compared to it's peers.

> it wasn't some architectural marvel compared to it's peers.

I don't think anyone is making that claim. it's just a good processor, especially for the era. it has weaknesses like any other processor.

The Z80 takes 4 clock cycles for an instruction fetch (or simple instruction) and 3 clock cycles for a memory access (if no wait states are triggered), while the 6502 does a memory access in each clock cycle and a simple instruction in 2 clock cycles (in the end it's always been about memory speed).

The Z80 may have been more convenient to work with because of the bigger instruction set and register bank, but a 2 MHz 6502 should easily be able to keep up with a 4 MHz Z80.

The ingenous thing about the 6502 was its simplicity. It had around 3500 transistors compared to 8500 transistors of the Z80, essentially "small and elegant" vs "big and brute force".

Disclaimer: I grew up on the Z80, but credit where credit is due ;)

> The 6502 was great for it's economy and simplicity. But it wasn't some architectural marvel compared to it's peers.

I've programmed both extensively, 6502 any time for me and 6809 over 6502 (if it has to be 8 bit).

I loved my old single sheet 6502 reference card that helped me through many things on the Apple ][+/][e -- see http://www.atarimania.com/documents/6502%20(65xx)%20Micropro...

The Motorola 6809 was (and still is) considered by many to be the most powerful and technically capable of the 8-bit CPUs. Its powerful PDP-inspired addressing modes, flexible registers, deep instruction set, layered interrupts and multiple stack pointers fully supported writing position independent, re-entrant code. This enabled native multi-tasking, multi-user operating systems to be written such as the Unix-like OS/9. Unfortunately, Motorola misread the potential market size and wildly overpriced the CPU for the first few years of its life, which is why it wasn't selected for any of the lower cost, high-volume home computers of the era despite its clear advantages.

Little known fact: Apple's initial Macintosh prototypes were based on the 6809 but the Mac was later upgraded to the the 6809's big brother the 68000 after Steve Jobs negotiated a very low price for the 68000. As a technical aside, the honor of best 8-bit CPU should correctly go to an even lesser-known 6809 variant, the second-source, Motorola-licensed Hitachi 6309. The 6309 was 6809 compatible and fabbed in CMOS allowing it to run almost twice the clock speed of the 6809, plus Hitachi added additional registers, instructions and optimizations even beyond the 6809.

"The added features of the 6809 were costly; the CPU had approximately 9,000 transistors compared to the 6800's 4,100 or the 6502's 3,500. While process improvements meant it could be fabricated cheaper than the original 6800, those same improvements were being applied to the other designs and so the relative cost remained the same. Such was the case in practice; in 1981 the 6809 sold in single-unit quantities for roughly six times the price of a 6502.[1] For those systems that needed some of its special features, like the hardware multiplier, the system could justify its price, but in most roles, it was overlooked."

https://en.wikipedia.org/wiki/Motorola_6809

Lucky for me Radio Shack inexplicably decided to use it in their Color Computer (I had a side job working in their stores so I had access to it) and when I started working full time for a bank a security guard there sold me his 'Dragon 32' micro which was a 1:1 clone of the CoCo. For the time this was a very interesting machine that used software where other computers used hardware, for instance, for audio in and out. The hardware was a bunch of resistors and a comparator (yay binary search) and replaced a whole bunch of costly ICs. I guess that's how they managed to keep the price of the machine down.

Total gaming

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