4 ms·

I'm not sure exactly what you're asking. The chip's inputs and outputs are wired from the chip's pins to metal pads on the die. These signals then routed (mostl

by kens 7y ago

I'm not sure exactly what you're asking. The chip's inputs and outputs are wired from the chip's pins to metal pads on the die. These signals then routed (mostly) through various metal layers to the transistors. For a MOSFET, the source and drain are in the silicon, while the gate is a polysilicon layer over top. The source, gate, and drain usually have contacts connecting them to the metal layer. I wrote a post explaining how some of the MOSFETs in the Z-80 microprocessor are wired up. It might help you: http://www.righto.com/2013/09/understanding-z-80-processor-one-gate.html http://www.righto.com/2013/09/understanding-z-80-processor-o...

bogomipz 7y ago
Wow, this post is really amazing!Thanks! I had a couple of question about the following: >"If input A is high, the first transistor will conduct and connect the yellow strip to ground (dotted line 1)" How does A being high connect the yellow to ground exactly if it doesn't cross the yellow strip? I'm not understanding what the dotted line represent I guess. >"On the left, the yellow metal line ties together parts of the gate. In the middle is the blue ground line, which is critical to the operation of the gate." Is the yellow metal line much much shorter than all the other vertical lines then? The other vertical lines seem to be longer in the pic. Why does input line "A" not cross the yellow metal line but the other 3 do? What is the actual function of the yellow vertical strip then?
- kens 7y ago
  (Note: this explanation only makes sense if you're looking at the diagram in the Z-80 article [1]). > How does A being high connect the yellow to ground exactly if it doesn't cross the yellow strip? The transistor gates are the green lines. Line A (polysilicon) is colored both pink and green; it's green where it is a gate and pink where it's just a wire. A signal can only cross the green line (gate) if the transistor is on. So if A is on, the yellow dot is connected to ground (via transistor 1). If B is on, the yellow dot is connected to ground (transistor 2), and so on. The yellow dot is a connection between the silicon and the metal strip (yellow) on top. The yellow metal strip ties together the three yellow dots, so it will be grounded if A or B or C is high. But that's only part of the gate. The output (where the resistor is) will be connected to the yellow metal strip if transistor 4 (D) or transistor 5 (E) is on. So the final logic function ends up being rather complex. The point is that MOS gates let you build complex AND/OR functions just as easily as a simple gate. > Is the yellow metal line much much shorter than all the other vertical lines then? Yes. The yellow metal strip is just internal wiring for the gate. The other vertical metal strips are long-distance routing from one part of the chip to another. For instance, the blue (ground) metal line goes all through the chip. > Why does input line "A" not cross the yellow metal line but the other 3 do? That's really just coincidence. A, B, and C are polysilicon wires, and they are separated from the metal layer by an insulating oxide layer. Think of the metal layer as an overpass above A, B, and C. On the other hand, if polysilicon crosses doped silicon (cyan), you end up with a transistor, so those crossings are very important. I indicate those crossings by changing the line color to green. It's hard to keep track of what's happening in the different layers. I probably should have made the explanation a bit more detailed. [1]: http://www.righto.com/2013/09/understanding-z-80-processor-one-gate.html http://www.righto.com/2013/09/understanding-z-80-processor-o...
  - bogomipz 7y ago
    >"The transistor gates are the green lines. Line A (polysilicon) is colored both pink and green; it's green where it is a gate and pink where it's just a wire." Thanks so much for this explanation. The input and output lines in schematic diagrams have always vexed me. The disconnect between how a transistor is often represented as a standalone 3D graphic such as you have above and how its actually implemented is silicon being the source of my confusion. Have you considered turning these z80 blog posts into a book? You have a great way of explaining things. Cheers.
that_jojo 7y ago
I just wanted to hijack this thread to say thanks for your deep dives into die reversing. They've really turned what always seemed like arcane runes into some sort of actual understanding on my part. Pretty much figured that would be impossible until this point.

by kens 7y ago

bogomipz 7y ago

Wow, this post is really amazing!Thanks! I had a couple of question about the following: >"If input A is high, the first transistor will conduct and connect the yellow strip to ground (dotted line 1)" How does A being high connect the yellow to ground exactly if it doesn't cross the yellow strip? I'm not understanding what the dotted line represent I guess. >"On the left, the yellow metal line ties together parts of the gate. In the middle is the blue ground line, which is critical to the operation of the gate." Is the yellow metal line much much shorter than all the other vertical lines then? The other vertical lines seem to be longer in the pic. Why does input line "A" not cross the yellow metal line but the other 3 do? What is the actual function of the yellow vertical strip then?

kens 7y ago
(Note: this explanation only makes sense if you're looking at the diagram in the Z-80 article [1]). > How does A being high connect the yellow to ground exactly if it doesn't cross the yellow strip? The transistor gates are the green lines. Line A (polysilicon) is colored both pink and green; it's green where it is a gate and pink where it's just a wire. A signal can only cross the green line (gate) if the transistor is on. So if A is on, the yellow dot is connected to ground (via transistor 1). If B is on, the yellow dot is connected to ground (transistor 2), and so on. The yellow dot is a connection between the silicon and the metal strip (yellow) on top. The yellow metal strip ties together the three yellow dots, so it will be grounded if A or B or C is high. But that's only part of the gate. The output (where the resistor is) will be connected to the yellow metal strip if transistor 4 (D) or transistor 5 (E) is on. So the final logic function ends up being rather complex. The point is that MOS gates let you build complex AND/OR functions just as easily as a simple gate. > Is the yellow metal line much much shorter than all the other vertical lines then? Yes. The yellow metal strip is just internal wiring for the gate. The other vertical metal strips are long-distance routing from one part of the chip to another. For instance, the blue (ground) metal line goes all through the chip. > Why does input line "A" not cross the yellow metal line but the other 3 do? That's really just coincidence. A, B, and C are polysilicon wires, and they are separated from the metal layer by an insulating oxide layer. Think of the metal layer as an overpass above A, B, and C. On the other hand, if polysilicon crosses doped silicon (cyan), you end up with a transistor, so those crossings are very important. I indicate those crossings by changing the line color to green. It's hard to keep track of what's happening in the different layers. I probably should have made the explanation a bit more detailed. [1]: http://www.righto.com/2013/09/understanding-z-80-processor-one-gate.html http://www.righto.com/2013/09/understanding-z-80-processor-o...
- bogomipz 7y ago
  >"The transistor gates are the green lines. Line A (polysilicon) is colored both pink and green; it's green where it is a gate and pink where it's just a wire." Thanks so much for this explanation. The input and output lines in schematic diagrams have always vexed me. The disconnect between how a transistor is often represented as a standalone 3D graphic such as you have above and how its actually implemented is silicon being the source of my confusion. Have you considered turning these z80 blog posts into a book? You have a great way of explaining things. Cheers.

that_jojo 7y ago

I just wanted to hijack this thread to say thanks for your deep dives into die reversing. They've really turned what always seemed like arcane runes into some sort of actual understanding on my part. Pretty much figured that would be impossible until this point.