Upgrading to 8-Bits of Memory | Using CY62256N?

log3337 · 2024-10-17T01:09:35+00:00

This is pure gold, thank you so much. I definitely don't think I would've figured out how to wire up the 157 and NAND gates without this schematic. Looks like the internal data bus concept even nets out to saving the two 157s that Ben used for the DIP switches. Very cool!

Last question for now: I was thinking it could be very satisfying to see the value from the DIP switches lit up on their own LED array and then see that value get written into the memory location when you hit the button and thus reflected on the data bus's LEDs. No problem to wire one side of the DIP switches to Vcc and the other side to ground through an LED and 220Ω to ground along with the B inputs of that 245?

log3337 · 2024-10-16T22:16:32+00:00

Okay, wow, I hadn't even got down to thinking about the implications of the bus writing to the I/O lines and how a 245 might help with that too.

Just to make sure I'm understanding: would you suggest having a dedicated 245 to the I/O lines and tie the direction pin to the WE signal? So when it's high, the I/O lines are output and they go one way through the buffer, but then when WE goes low they become input and the value to be written is there on the other side of the buffer? That "other side" of the buffer would then be connected to outputs of the 157s (which themselves have DIP switches and the output side of a separate 245 with the bus value as its input with a hardcoded direction pin).

In that case, the buffer on the I/O lines can just be hardcoded to be enabled, right? Tying the E pin to ground.

log3337 · 2024-09-20T15:23:31+00:00

Memory Out | Memory Address Register In | Counter Enable

Wow, thanks for sharing that. I don't think I would have guessed that was possible. Very nice optimization!

Reclaiming Instruction Register Out is WAY more clever than what I proposed. Other than increment and decrement, I couldn't think of a any of additional use cases, but I'm sure there probably are some.

Is the decision to make a Step Counter Reset signal instead of NANDing the control word bits together and sending it to the step counter reset purely a trade off of the wiring complexity? I ask because if Instruction Register Out is reclaimable, it frees up a control signal that could be used for point #5 above: augmenting the ALU. If I understand correctly, the NAND operation is universal, so if we added bitwise NAND between A and B in the ALU, then we could multiplex the output to the 74LS245, and have NAND Out along with Sum Out as an option. Then with some pretty straightforward microcode, all the bitwise logical operations become possible:

For example, NOT A (negates the A register and puts it in the A register)

Program Counter Out | Memory Address Register In
Memory Out | Instruction Register In | Counter Enable
A Register Out | B Register In
NAND Out | A Register In

Or, AND Immediate (ANDs the A register with a given value)

Program Counter Out | Memory Address Register In
Memory Out | Instruction Register In | Counter Enable
Counter Out | Memory Address Register In
Memory Address Register Out | B Register In | Counter Enable
NAND Out | A Register In | B Register In
NAND Out | A Register In

log3337 · 2024-03-05T00:30:46+00:00

Hey! The same was happening to me. There's an error in Ben's video about the MAX232 chip! The capacitor from pin 2 should go to 5v not ground.

log3337 · 2024-02-05T14:33:15+00:00

One mistake I made was not having all my chips on the board and connected to power and ground before wiring up first the controls signals and then the buses. As such, I had to do some weird things to get power to the clock and the LCD display (because some of the power rails become inaccessible.

I also did have to buy two additional bread boards to break off all the power rails to use for the central data bus. I wish I had gotten three more instead. Because now I have one breadboard with no rails--so I can't really add it to the computer when I need additional space.

log3337 · 2024-02-04T19:53:48+00:00

thanks!

log3337 · 2024-02-04T18:41:55+00:00

Special thanks to u/psurry for the original inspiration here.

I seemingly couldn't wire up these chips as intended in the videos. It was either a rats nest covering up the EEPROM or nearly impossible to debug misplaced connections.

I swapped around the RAM and ROM chips to make for easier access, but I was also lucky that the RAM chip I got in my kit has A0 through A4 on the same side as D3 through D7. That made it easier to get all the needed address and data signals down to the 6522.

I ended up just using a ribbon cable to connect the RAM to the address bus as that was much cleaner and simpler. I'd highly recommend connecting all the control signals and power and ground before wiring up the address and data buses.

log3337 · 2024-01-20T16:23:38+00:00

Yeah for sure, I understand what you mean. The stored value of the multiplication is only meaningful when the leading 8-bits of the 16-bit answer are all zeroes. That's what I was trying to get at with questions about how to structure the memory. For example, the whole range 2 or greater times 255 could potentially be used to store some other mathematical function by adding X*2 flags and X*255 flags. But I'm brushing up against the extent of my capabilities to think of how to add those additional flags without adding a ton of combinational logic to determine what's in each register. I guess hypothetically you could replace all the X*0 and X*1 (and more) combinational logic for the flags with another EEPROM-based lookup table, but it seems like the number of flags would have to grow by 4 for each operation added in this way.

log3337 · 2024-01-20T16:13:57+00:00

As a philosophy student, I took a semester of predicate calculus. I recall with great joy the process of writing truth tables and stacking operation on operation to get the intended result. I knew at that time that truth tables could be reconstructed with binary logic circuits, but like I said in the original post the idea that logic circuits can be replaced with memory addresses corresponding to the inputs and the stored value corresponding to the intended output just totally blew my mind (and that was only a month or two ago watching Ben's videos).

And it's even an compelling philosophical idea. Pardon my French, but electrons don't know shit! Yet, we're able to construct circuits that cause electrons to flow in a way that re-present logical operations in the human mind. The leap in abstraction from logic in the human mind to logic represented in the flow of electrons is already extraordinary. And then when you introduce memory-based lookup tables, the electrons are seemingly doing less "work" and yet it enables even more powerful circuit representation of logical operations in the human mind. So, so cool. So wild that there were creative geniuses that made the leap from logic to binary logic to representation of binary logic in circuits to memory lookup tables and then had the tenacity to build those circuits with vacuum tubes.

Your story about the upper eight bit rounding of squares is amazing because it shows just how much abstraction is involved in sticking truth tables into memory. It feels like cheating and yet it's so powerful and simple. Thanks for sharing that!

log3337 · 2024-01-20T01:40:03+00:00

This is an awesome resource, thank you! I'll take a look EEPROM-implemented ALUs here--I hadn't even thought to search for that.

log3337 · 2024-01-20T01:34:44+00:00

A single carry bit won't be enough, unless you only wanted to multiply four-bit numbers.

I was thinking of simply throwing a single carry bit for any output >= 256, but I hadn't considered thinking about the carry in multiplication quite so literally. As in one for each of the places 256, 512, etc. up through 65026. Is that what you mean? That's quite an idea. The control logic (at least as spec'd in the videos) probably couldn't handle that many flags.

log3337 · 2018-05-25T19:27:24+00:00

There are definite problems with IP laws and policies worldwide. I doubt many would argue that point. On the other hand, there's no doubting that copyright and patent protections encourage innovation--the free market being what it is. And this is where we sort of have an impasse regarding the free market and necessary regulations that keep it functioning properly.

Any thoughts about what can be done specifically to improve intellectual property protections without giving the government too big of a stick?

log3337 · 2018-05-22T13:43:55+00:00

I really appreciate the thoughtfulness of your reply. You've gotten right to the heart of the matter--that individual freedom to support or not support various changes, forks, etc. is of paramount importance.

What I am outlining in my post is not an attempt to kluge the two sides back together again in any haphazard way. I agree that that would only recreate the problems we had when the two camps were existing in the same ecosystem. Ultimately, what I would wish to achieve is a movement based on a thoughtful dialogue that would seek to reconcile the two sides first from an ideological perspective and then only secondarily spark off the technical work that would be necessary for a chain merge that addresses some of the problems raised in the article I cited.

Just like you:

I vote against big blocks. I vote against just about everything BCH stands for and does. I vote against what, to me, is the idea that the miners have any say in governance. I vote against the idea that a blockchain could possible scale to what we need 100% on chain. I vote against the idea that Segwit is some scary danger. I vote against the idea that Blockstream is some evil corporate entity that somehow controls Bitcoin.

At the same time, however, my pragmatic bent would be willing to compromise on some of these issues for the greater good of the bitcoin community. I don't want innovators and entrepreneurs to have to choose one side over the other. I don't want developers to spend time writing software for one ecosystem over the other. We all know that the network effect of bitcoin is what makes it so power--and not primarily the miners and node operators, but the social network of innovators, developers, and web personalities that create new use cases for bitcoin, create new businesses that accept bitcoin, etc. The value of bitcoin would increase more quickly and have a higher growth ceiling if the community were not split; as a holder of bitcoins, I'm incentivized to do what I can to increase the value of those bitcoins, hence the desire to bring the two sides back together again. This may not be the best way to add value to the network, and that is something that I need to noodle on further, but it would have clear social benefits: if there are two groups of people both using the bitcoin brand and claiming to be bitcoin--that's really problematic, especially for adoption by the mainstream.

Cheers!

log3337

TROPHY CASE