Inside the Famicom | 02: The 6502 CPU

Welcome to the second video in my multi-part series on the Famicom. In this video, we’re going to take a closer look under the hood, as we dive into the Famicom’s central processor and learn what makes it tick… literally! We’ll talk about some of the interesting background associated with Nintendo’s use of the 6502 and start exploring the mechanics of Ricoh’s 2A03/2A07 chip.

Links Referenced in this Video:

[play_history]

Okay so on the BCD removal thing: To my understanding this was a redesign that Rockwell did first. MOS second-sourced production of the 6502 and variants to Synertek and Rockwell (a common practice in the industry at the time). Rockwell made modifications to the chip and Rockwell sub-licensed the rights of their design to Ricoh.

MOS engineers have claimed that Nintendo stole the 6502 because they weren't getting direct payments, but anything they would have gotten would have gone through a long chain through Rockwell. Such are the salad days of early microprocessors.

[ZipplyZane]

What I love is that the lack of hardware BCD is why Tetris eventually crashes. It's the software BCD that winds up eventually taking too long to calculate and results in corruption.

So that whole Tetris crash thing made something this old relevant again.

Also, I love that it's the same chip with that line cut, and that was enough back then to say it was a different chip. That's the only reason it was left out. It allowed the copy to be legal.

[AlexanderEmashev]

Wow, such a thorough and clean explanation of how the CPU works. Animation really helps to understand what happens and why. Thank you! Looking forward to watching the next part.

[scotchnichols]

I've really enjoyed your deep dives into the Famicom so far. Looking forward to the next one.

[HSTVizle]

These videos are awesome! My favourite lecture was Microprocessors in college, we've studied similar 8-bit CPU desings. Keep going Ken!

[SplitHouse]

This is a great video to watch while I'm working on my NES emulator project! Thanks!

[rudy]

Loving this series! Watching along as I plan to AV mod my newly acquired Famicom!

[willllbert]

Fantastic series! Looking forward to learn more 😊

[wizzo-bi]

Really enjoyed this! Not a huge fan of the games on these consoles but I have a huge soft spot for the 6502

[omarhossam]

This is so goated omg. What a great video

[TheMikeyb]

Love this. Keep 'em coming. Thank you.

[iwanttocomplain]

There's something I've been trying to remember about 6502 bus requests for a while and not into all the resarch and it's really the key issue I have with the 6502. The SNES has 128KB of working ram. People think it's all available. But it's not.

I'm also quite proud of myself for predicting two 8KB buffers in the NES by counting the numbers and not figuring out how it could have 2K of work and video and also 8K, but slower.

[chansonjoy]

Interesting, in fact it's very close to modern MCU architecture, except very limited IRQ resource and probably doesn't support nested IRQ at all.

Modern MCU usually also come with NMI IRQ, but I found it hardly being used, because there are many other high priority IRQ available. I wonder what's the scenario of NMI in 6502.

[leandrormor]

Thanks for the content. If the CPU divides the master clock input, does that affect the output?

I'm curious to learn what clock reference the others components expect since cpu internally uses a different clock.

[cosmefulanito]

Since the Z-80 was and still is today the most used processor in the world (enbedded today), I don't understand why people in the USA are so fixated on the 6502.
Good video.

[docwhogr]

the nes inner working was explained by many, i think someone should give love to the other consoles. you did an excellent job though
when you said go make something cool i went and fill the icecube tray in my fridge. does it count?

[mwk]

So... if the Famicom 2A03 chip has 16 bits wide address bus does it mean that it really is a 16-bit CPU? (hello Atari Jaguar!) 😎

[JamesSjaalman]

IMHO Great Britain did not have the PAL standard.

[stempek]

What's the software shown at 2:26 mark?

[ssl]

Chip masks are only protected for 10 years and the Famicom came out before the mask law was even passed. It would be foolish not to use the masks or to pay a license for something in the public domain. Do you send Youtube money for the free music in your videos?