How to Build 1 Bit of RAM Using Transistors
avrillion.com
How to Build 1 Bit of RAM Using Transistors
1–10 of 46 posts
Re: How to Build 1 Bit of RAM Using Transistors
#2Four transistors? I can do it with only 2, it's called bi-stable circuit:
Re: How to Build 1 Bit of RAM Using Transistors
#3Four transistors? I can do it with only 2, it's called bi-stable circuit: https://en.wikipedia.org/wiki/Flip-flop_(electronics)
It's great to add relevant information, but in the future, could you please do it in a way that greets and expands on what you're replying to, rather than one-upping or putting it down? The two styles of responding have opposite effects on discussion: one opens it up for further exploration, while the second constricts it or closes it. In improv, that is called "blocking": https://improwiki.com/en/wiki/improv/blocking. You probably didn't mean it that way, but intent doesn't communicate itself. Since a comment's impact on future discussion is determined by how others hear it, the burden is on the commenter to disambiguate [1].
The value of an HN comment is its impact on current and future discussion, or (to put it in a pseudo-technical way) the expected value of the subthread it forms the root of [2]. I've been struggling for a way to explain this that doesn't sound smarmy (like "be nice" or "tone"), since it's not about being nice. It's about what leads to richer improvisation and curious conversation, which is what we're trying to optimize for here [3].
Edit: elsewhere in this thread are some great examples of opening-up responses:
https://news.ycombinator.com/item?id=22798780 ("even more interesting...")
https://news.ycombinator.com/item?id=22798746 ("I once...")
If you ask yourself and sense into what kinds of responses such comments invite, you'll get the spirit of what we're going for. I don't mean you personally—I mean all of us. This is a community project.
[1] https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...
[2] https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...
[3] https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
Re: How to Build 1 Bit of RAM Using Transistors
#4Isn't this just a flip flop?
Re: How to Build 1 Bit of RAM Using Transistors
#5I once made a single-transistor latch by accident. It acted as a single bit of memory and retained its value for weeks until I got bored with the project.
I had been making magnetic snap-together circuits, so I had a bunch of small PCBs with simple 2- and 3-pin footprints and holes that I soldered neodymium disc magnets into.
I put a big TO-220 N-fet on one of them, and stuck it to a laminated whiteboard so that the magnets stuck without shorting together, then I hooked it up to an LED as a simple high-side switch.
When I bent the transistor so that its metal plane rested against the magnetic whiteboard, its gate would latch after briefly tapping either V+ or ground to the magnet which was connected to the pin. When the transistor's metal plane was perpendicular to the board, it didn't latch. Disconnecting and reconnecting the LED didn't perturb the 'saved' value, and neither did removing power overnight. And the same thing happened with a similar P-fet connected as a low-side switch.
It probably wasn't a "real" latch; it was a very over-sized transistor with low gate capacitance, and I didn't try it with something like a 3904. I think it might have had something to do with the principles behind nonvolatile ferroelectric RAM, but I never did get to the bottom of it.
Re: How to Build 1 Bit of RAM Using Transistors
#6Four transistors? I can do it with only 2, it's called bi-stable circuit: https://en.wikipedia.org/wiki/Flip-flop_(electronics)
but that's not what he's building, he's making the "gated D latch" from your reference - something that's much more useful in real-world circuits than the minimal 2 transistor flop that you call out
Re: How to Build 1 Bit of RAM Using Transistors
#7An even more interesting exercise would be to implement a DDR5 driver circuit for the 1 bit of RAM. Typical DDR5 interfaces take hundreds to thousands lines of Verilot/VHDL so quite a few transistors will be needed.
Re: How to Build 1 Bit of RAM Using Transistors
#8A capacitor is 1 bit of memory.
Re: How to Build 1 Bit of RAM Using Transistors
#9A capacitor is 1 bit of memory.
Yes - I think that is what DRAM is at its core - and requires more refresh to keep the charge on that capacitor - versus SRAM which is a more complex latch transistor based approach (which also happens to be faster and less power intensive - but also more expensive per bit).
Re: How to Build 1 Bit of RAM Using Transistors
#10I once made a single-transistor latch by accident. It acted as a single bit of memory and retained its value for weeks until I got bored with the project. I had been making magnetic snap-together circuits, so I had a bunch of small PCBs with simple 2- and 3-pin footprints and holes that I soldered neodymium disc magnets into. I put a big TO-220 N-fet on one of them, and stuck it to a laminated whiteboard so that the…
FWIW I'm told that decades ago latches were implemented as a tristate driver followed by an inverter or buffer. The source & drain cap, along with gate & wire cap, acted as the memory.