Confirmed the MOS 7600/7601 Pong chip is a true microcontroller

http://oldvcr.blogspot.com/2022/09/confirmed-mos-76007601-pong-chip-is.html

by kens • 4 years ago

151 48 4 years ago

oldvcr.blogspot.com

kens9• 4 years ago

It's not my blog post, but I can answer questions about the chip.

classichasclass2• 4 years ago

Thanks again, Ken, for your help with this!

philistine2• 4 years ago

How close is it to the chip in the VCS? Was it a step towards the 6507?

kens9• 4 years ago

The 6507 chip was essentially a repackaged 6502 microprocessor. The game chip is pretty weird, with a custom microcontroller and a bunch of specialized circuitry. So I don't think there is any connection between them.

TedDoesntTalk2• 4 years ago

I had the Coleco Telstar arcade and all its cartridges, thanks to my parents. I was just a young kid at the time. Thank you for this deep dive into a chip that shaped my childhood.

chclau• 4 years ago

If I were you, I would try to reach to the blog poster.

kens9• 4 years ago

I've been working closely on this chip with the writer of the blog post (and with Sean Riddle who took the die photos) for the past month.

classichasclass2• 4 years ago

That would be me. Ken was very helpful.

ksherlock• 4 years ago

"The way the paddles in particular are drawn is especially ingenious; in fact, the firmware doesn't even need to position them. The paddle controls are simple potentiometers feeding into an R-C circuit (external to the chip, not shown here) that discharges at a rate based on the pot's resistance. This then feeds into an on-chip comparator in the region marked "paddles," delaying drawing the paddle a number of scanlines based on the pot's position until the comparator triggers, thus eliminating the need for a more complex solution like an A-D converter (cheap!) and automatically drawing the paddle at the proper location without any intervention from the firmware."

I love it!

philistine2• 4 years ago

If you want the least amount of lag possible, you now know which device to turn to. I'm thinking of the famous lag table of character entry for 80s 8-bit computers and modern PCs.

tuukkah• 4 years ago

This device should be remade for a 120 Hz display to halve the maximum lag from 17 ms to 9 ms.

alexdbird• 4 years ago

Using these machines on a 2022 display adds so much lag, it really makes them unplayable. On a CRT the connection between your movement and the paddle on screen is so immediate and undamped, it can be quite a powerful experience as you embody it despite its crudity. Helps to understand how simple games like this were so popular.

I have a few, but sadly I don't have the space to keep a CRT monitor too.

EvanAnderson2• 4 years ago

It's a nice hack. I think this is how Woz did the Apple II paddles, too (albeit with discrete components and a timer IC). It sounds familiar.

kens9• 4 years ago

Yes, the Apple II also uses a resistor-capacitor timing circuit to determine the paddle position. The big difference, however, is that the Apple II uses the timer and a counter to produce a paddle position 0-255. Software can then use this value to e.g. draw a paddle at a position on the screen.

The game chip, on the other hand, doesn't produce a value. Instead, the timer is synchronized to the screen drawing, so when the timer fires, it indicates to draw the paddle now. So the system never has the paddle position as a digital value and there's no register that holds the paddle position.

randyrand• 4 years ago

very cool to see the engineering of that time.

justinlloyd7• 4 years ago

The MOS 7601 was the first CPU I learned how to write code for, circa late 1977 to early 1978. I would scour jumble sales for broken pong games and the other, more sophisticated console variants to cannibalize for parts, with one conversation about haggling with another buyer over who got what parts leading to a job.

There were several machines of the time that had pluggable cartridges, from Binatone, Telarude?/Telalude? (French or Italian company I recall, I forget), Telstra/Telstar, again, I forget, it was 45 years ago, along with many others, where the display circuitry, power and joytsticks were all on the main board, but each cartridge carried its own CPU and ROM, which was the fashion back in the day.

They were an absolute bugger to write code for, no complex ALU to speak of, no register storage, no RAM, you sort of just chased the CPU with a stream of instructions, stored stuff in decay buffers (you want a countdown from 10? charge up that cap for a brief period of time then let it leak) or on the display output circuitry that you could read back if you needed. If your code went wrong, you never knew it.

You were mostly bit-banging analogue circuits to get anything to display, same for the audio, though it could also talk to some AY audio synthesizer.

I recall the 7601 had a reasonably short lifespan in the marketplace for a variety of reasons.

There were two datasheets for it that were the bible, there might have been more but I only ever had access to bad photocopies of those two. One was the usual electrical characteristics and the other was the instruction set with the usual timings, delays and addressing modes.

The addressing modes were stupidly simple by the standards of today. There were EPROM variants (gold pin variant IIRC) available that you wiped with a strong ultraviolet light, but generally you had an off-board EEPROM and you tied two of the pins high to let it know it should use the external EEPROM.

When I tell people my first game I wrote fit in less than 500 (8-bit) bytes, they wonder how that is. The game was never released but Race Electronics and their desire to cash in on this new fad and exploit the younger, more gullible version of me, did give me my start in video game development so I am thankful for that, in a way. The next game I wrote fit in 2KBytes and I had the luxury of using a 6502 CPU and access to actual RAM on a CBM PET.

HailTheGreenOne• 4 years ago

What was the game? Could you possibly run it again?

tssva• 4 years ago

This comment discusses how ball and paddle collision detection worked but leaves open the question of how the ball position was known. https://news.ycombinator.com/item?id=32862403

Given your experience programming for it can you provide any insight to how this may have been done?

diydsp• 4 years ago

Yeah! when he mentioned making a timer by charging a cap and letting it discharge... that could apply to the ball position registers... it could also explain how they did various angles when there's no obvious multi-bit ALU.... varying dis/charge ratio...

kens9• 4 years ago

Are you sure you're talking about the same chip? None of this is consistent with what I see on the die.

justinlloyd7• 4 years ago

It is possible I am misremembering, and possibly even smushing two memories of completely different systems together. We are talking ancient history and I only worked on these systems for a few months at most. On your die photos or block diagrams that you are referencing, are there references of where the graphics were hard-coded into the system? If I wanted to show the playfield, I could strobe an address that would draw the playield? If I wanted to show a score of 9 for player two, I could strobe another address? I recall that the playfield was frequently mirrored (left-right or top-bottom), so it was possible to combine bits of playfield for different games.

justinlloyd7• 4 years ago

Following up on this: I recall the microprocessor came in a plastic and ceramic variant, and the ceramic variant, I seem to recall, had an EPROM window on it (though my memory is a little fuzzy on that detail). I do recall that GI/MOS had an ICE that closely resembled the one for the Intel MCS-4x series of microprocessors, i.e. expensive and not available to anybody without a minicomputer on hand. GI MicroElectronics and AMI MOS put out a physical catalogue of components each year that I would pore over as a kid, along with the Maplin's catalogue, Siglent, and a few others.

Did anybody think to ask the original chip designers for GI out of Scotland? Many of them are on LinkedIn, though now retired. It is pretty easy to track down the GI MicroElectronics people.

Go grab a couple of back issues of Practical Electronics from the 1970's and a Maplin catalogue from the 1970's, they contain almost all of the GI and AMI MOS parts, including data sheets and example code. There's probably PDFs online by now. The GI catalogues and the MOS catalogues of the day also have all the datasheets and block diagrams in them and contain every non-custom part they made, though many parts could be customized to need. The General Instruments MCS/MPS (Microprocessor Ceramic System/Microprocessor Plastic System) 7600 is based, AFAIK, on the MCS5600 with extra bits. <strikeout>I recall that AMI MOS listed all their microprocessors under the "S" range, e.g. S6800.</strikeout> But again, fuzzy on the details and I wasn't privy to a lot of information and the internet back then wasn't what it is today (That's a joke). US Patents were definitely filed for these devices by GI MicroElectronics and AMI MOS, even though, technically, the 7600 variant was developed in Glenroathes. A quick internet search shows that the patents would be the 3,800,000 to 4,000,000 range based on the date of issue. Just need to search for the designers' names, or the corporation filing.

And if I have incorrectly stated anything, or lead you astray on details, it is not intentional. It's that 45 years later I didn't think I'd have to recall details about my middle-school and high-school years and my first forays in game development and electronics. And if it is a bit incoherent I blame only being on my third coffee of the day and trying to dredge up half-forgotten details. <insert Gandalf "I have no memory of this place" meme>

justinlloyd7• 4 years ago

Also look up old issues pf Microcomputer Digest, circa 1974 to 1976, same era as the MOS catalogues, as I am pretty sure the various processors were covered in there. Everyday Electronics or Practical Electronics, or one of those variants also included schematic and detailed instructions on using the "Pong on a chip" devices to make your own home console, though I don't recall which microprocessor they used.

tralarpa• 4 years ago

There were datasheets with the instruction set? But why does the article say that they were, until very recently, not sure whether it's a microcontroller?

justinlloyd7• 4 years ago

I don't know. But really, how could somebody not know it was a microprocessor? It's in the name. MPS and MCS. MOS and GI didn't randomly and winsomely name their parts like it was a Node package on github.

retro64• 4 years ago

...which was the fashion back in the day.

Not sure if this was an intentional simpsons reference but it made me laugh anyway given the context.

(seriously though, thanks for taking the time to write this up - I find these firsthand experience ramblings fascinating).

dannyobrien• 4 years ago

i had a binatone pong game that sounds like it was based on this chip. It had a bunch of variants of pong you could play based on moving a couple of physical sliders -- squash (bounced off a wall), football (two bars per player), etc.

The crazy thing was that if you turned the sliders just right, you could also play "off menu" games which had combinations of the attributes of the official ganes. I guess this was down to some of the tricks described here. It certainly confused me a lot when I learnt to program: you can't just compose two games together by half-clicking on an option!

TedDoesntTalk2• 4 years ago

you could also play "off menu" games

This is called “circuit bending” now and has quite a following.

I did it with the Atari VCS (now called 2600) quite a bit. The Spider-Man cartridge had some great weird incarnations by moving power switch half-way, as did a few other carts.

NobodyNada2• 4 years ago

I’m reminded of that scene in Battlestar Galactica (2004) where Starbuck cuts open a crashed Cylon raider, climbs in, and finds it’s actually organic rather than robotic — instead of the neatly-organized metal and wires and computers you’d expect to see in a hi-tech starship, it’s full of messy flesh and blood and organs.

In the same way, here they cut open a microcontroller and instead of finding a neatly organized CPU with all the usual recognizable bits and software written in a straightforward ISA, there’s this weird, surprisingly analog amalgamation between hardware and software, between control and data. It’s not obvious how anything even functions because it’s so alien compared to our nice, clean, modular general-purpose CPU. Instead it feels…almost natural, like the hardware and software grew and evolved together as a single unit (which, to be fair, they probably did). It’s beautiful and terrifying at the same time.

At least, that’s how it feels to me as a (sleep-deprived) software engineer. Maybe to a hardware guy, this is just Thursday.

moffkalast• 4 years ago

as a (sleep-deprived) software engineer

So say we all.

mmastrac• 4 years ago

The line between "chip" and CPU has always been a bit blurry. Anything that deals with USB or any other complex protocol is probably based on a tiny CPU (8051s are still weirdly common).

Software runs the world, but some of it is just cleverly disguised as hardware.

sidewndr46• 4 years ago

I can second this, I remember looking at the spec sheet for an early USB interface chip. It includes a complete processor. No MMU, but the datasheet even showed how to prevent someone from reading the contents of the ROM.

retrac• 4 years ago

As early as the mid-1970s, minicomputers and mainframes started incorporated microprocessors for things like system monitoring, booting, and peripheral interfaces. In 1981, the original IBM PC's keyboard had a 8048 microcontroller internally to handle communication with the PC. Architecturally, this is still how it's done, usually just all shrunk down to a single IC now. Pretty much any expansion card or USB device will have a microcontroller in it, possibly multiple.

NobodyNada2• 4 years ago

Oh, for sure. But my surprise is less because there’s a CPU in the chip, and more because the CPU is so weird, and so tightly integrated with the rest of the chip, rather than being a “normal” general-purpose processor that communicates using a set of cleanly-defined I/O interfaces.

londons_explore• 4 years ago

This seems like a lot of transistors for such a simple game....

If they could reduce the number of scanlines on the monitor, they could get many hundreds of clock cycles per pixel, and then do everything in software. 512 instructions seems quite possible for that - compare to 'boot sector games' which run in about one third of the space.

kens9• 4 years ago

There are a couple of problems with that approach. First, the game uses a standard television, so you can't change the number of scanlines. Second, the pixel rate is about 1MHz, so you'd get about one clock cycle per pixel with a processor of that era. Of course, doing everything in software was a long-term solution.

colejohnson66• 4 years ago

512 instructions seems quite possible for that - compare to 'boot sector games' which run in about one third of the space.

Except a (boot) sector is 512 bytes (assuming x86)? Technically 510 because of the two bytes to indicate that it’s bootable, but that’s quite a bit more than 1/3 of 512.

lbriner• 4 years ago

I am still genuinely amazed about what was achieved in this era, bearing in mind that these things took years to develop so started much earlier when most people probably had never heard of a transistor.

Despite the infancy of the industry, these people not only designed an enormous electronic circuit but had to work out how to achieve compatability with inputs and outputs as advanced as graphics, how to store data in memory, had to perform a tonne of debugging and had to get this thing etched onto silicon and then produced at scale.

Wow, just wow.

PaulHoule• 4 years ago

I see it the other way around.

Steve Wozniak implemented Breakout with fewer 50 small scale integration chips, which is a fraction of the complexity of a 6502 CPU. I mean, a build system for a trivial JavaScript app is probably more complex than the software the flew the Space Shuttle

Confirmed the MOS 7600/7601 Pong chip is a true microcontroller

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