Electronics/CPU question

[HarryW]

Not really important this, I was just wondering...

Roughly what is the minimum number of transistors needed to make a very basic CPU?

I know this is a bit of a stupid question, but I was just sitting here pondering and thought I'd see if anyone knew better. Are we talking thousands, tens of thousands, hundreds of thousands or what? I have no idea how you would construct a register. How do you do that?

Ah well back to pondering more meaningless questions...

[Sam Finch]

There's a table with how many transistors different chips have at http://www.ece.uiuc.edu/ece291/class-resources/opcodes.html the 4004 introduced in 1971 had 2,300 transistors, It says that was the first one to do arithmatic etc, so 2,000 is probably your lower limit.

What do you wanna bet it's 2k? 2048

[HarryW]

Oh, cool, thanks Sam :) I don't suppose there would be some sort of circuit diagram for the 4004 anywhere I can see would there? Probably asking a lot. I'd like to know how they make registers. I've seen basic ALU stuff, and opcode decoders, I'm wondering how they make addressable memory.

The 4004 was first used in the old Commodore Calculators.
You could probably find a schematic on the net someplace.

[kovan]

HarryW what you gonna name your cpu as?
Haariod? :)

[Sam Finch]

DefFarm I wi;ll bet everything I have that it's not 2048.

Harry I've seen the thing they use, I can't remember it exactly. you can make a 1 bit address bus quite easily using 2 and gates an Or gate and a not gate (so you have bit B0 and bit B1 as your memory, A as your address bit and R as the result

R = ( B1 && A ) || (B0 && !A)

put 8 of these together connected to the same A and you've got 2 bytes of addressable memory.

then if you want 2 bits have similar circuits controling the B1 and B2 inputs to the R circuit, keep going for all your address space needs.

[HarryW]

I see... so you would store each bit using a simple flip-flop would you?

The reason I'm askig all this is because it's been ages since I did any electronics, but with a recent course I did I had to write microcode and deal with registers, so I got a much better understanding of how the whole thing works. I'm kinda tempted to get the soldering iron out again. The closest to electronics I've got to in the last couple of years is chipping Playstations.

[Robbo]

I know the old one can be chipped but can the new PSone be done the same i know it is 1/3 the size of the first and there may not be much room but can it be done

just asking if any one knows, but if u do post it here????

[marnitzg]

Originally posted by Robbo
I know the old one can be chipped but can the new PSone be done the same i know it is 1/3 the size of the first and there may not be much room but can it be done

just asking if any one knows, but if u do post it here????

Whats this? Illegal discussions? Tisk Tisk!

(P.S. I believe so)

[HarryW]

Robbo, it is most certainly possible to chip the new PS One consoles. I expect the shrunk down size makes things a little more awkward than before, but it's only 3 wires (7 for the stealth) so it's no big deal. The simplification may have helped, since the PS One probably has less components and might be easier to disassemble and reassemble.

Pre-programmed mod chips should cost no more that £2 (+P&P), but of course if you cock it up then you run the risk of breaking your Playstation ;)