I wonder if it could be done in a similar way but run full speed? From the FAQ:
> Does it run at the full speed of an original 6502 chip?
>
> No. The MOnSter 6502 is relatively slow compared to the original, thanks to the much larger capacitance of the design. The maximum reliable clock rate is around 60 kHz. The primary limit to the clock speed is the gate capacitance of the MOSFETs that we are using, which is much larger than the capacitance of the MOSFETs on an original 6502 die.
I think I'm imagining most of an entire motherboard of something similar to the C64 or Apple ][ implemented this way, wall mounted along with a display and controls, with a classic software library.
This is one of the key things that integrated circuits bought you, when moving from discrete to integrated circuits you could switch the transistors faster because they needed either less current (TTL) or less charge (NMOS/CMOS) to switch. Or conversely, the same charge could switch them faster.
So if you look at the highest performance discrete computers of their time, things like the CRAY the CDC machines, etc. You'll see that they consumed larger and larger currents to achieve the switching rates they needed to achieve and increasingly exotic cooling systems (with the Cray's flourinert systems being pretty damn awesome).
I find it fascinating to walk from the ENIAC to the 704 to the B5500s, and PDP-8's and 11's, to microprocessors to systems on chips. Each step in integration let you make things smaller and run them faster. It wasn't until Moore's law broke down in 2004[1] and the world became multi-core that this really stopped happening.
I saw this on display at the NYC maker and also asked about what it would take to run full speed. He said the gate capacitances of discrete MOSFETs are 100's of times greater than the tiny ones in a chip. This would require traces that could handle dozens of amps and a power supply for the whole board that could provide over 100 amps. So not really feasible - but then again, neither is building a circuit board to duplicate a chip
It could be done if you switched from MOSFET to BJT. That's how they built discrete processors back in the day. At least low double digit MHz clocks would be doable as long as you pay attention to trace lengths, capacitance, power consumption/heat, etc (in other words, all the same design considerations they had when BJTs were state of the art)
That said, I think the objective was to duplicate the processor rather than the systems it ran in so their existing MOSFET design is true to that.
The N-type enhancement mode MOSFETs it uses require a positive gate-to-source voltage to turn on, and are turned off by pulling the gate-to-source voltage down to 0v. The gate itself forms a capacitor which must be charged to allow the gate-to-source voltage to increase and the MOSFET to turn on. Running a higher voltage than the standard 5v (SOT-23 small signal MOSFETs often can handle 20vgs, depending on the specific part) would allow the gate capacitance to charge much faster and the MOSFETs to turn on much faster. However, the clock speed will still be limited by how quickly that gate charge can drain to 0v in order to turn the MOSFET off.
I wonder if it could be done in a similar way but run full speed? From the FAQ:
> Does it run at the full speed of an original 6502 chip? > > No. The MOnSter 6502 is relatively slow compared to the original, thanks to the much larger capacitance of the design. The maximum reliable clock rate is around 60 kHz. The primary limit to the clock speed is the gate capacitance of the MOSFETs that we are using, which is much larger than the capacitance of the MOSFETs on an original 6502 die.
I think I'm imagining most of an entire motherboard of something similar to the C64 or Apple ][ implemented this way, wall mounted along with a display and controls, with a classic software library.