> The entire Zilog those days had 11 people. > It took one year and one month from the kick-off meeting to fully working silicon. > We basically got $500,000

> The entire Zilog those days had 11 people. > It took one year and one month from the kick-off meeting to fully working silicon. > We basically got $500,000 the first financing of the company. And I promised to Exxon that we would get on March 9 that we would get the first working CPU and that I would spend $400,000. And Shima was able to get the Z80, the first working Z80 on March 9. And that was incredible feat. And we spent $400,000. > In order to support the high-speed task switching, in the beginning I asked to complete two sets of register files including the program counter. But it was too complicated to customer. > I remember one event that sticks out very clearly, and that is that we were just ready to the put the mylar into the layout, when we found a bug in the simulator, in the software - I mean, in the hardware. And we basically went to Shima and said "We have to stop, there's a bug in the chip". Shima looked at us carefully, and thought for a couple of seconds, and said, "No, no problem, we just have to put a contact here." And it was the most amazing thing that we would take the logic error and turn it into a physical fix in a just a few seconds. And sure enough when it was fixed, and when the chip came out, it was bug-free. > Faggin: Yes, we were concerned about others copying the Z80. So I was trying to figure what we could do that that would be effective, and that’s when I came across an idea that if we use the depletion load the mask that doesn’t leave any trace, then I could create depletion load devices that look like enhancement mode devices. And by doing that we could trick the customer into believing that a certain logic was implemented, when it was not. Then I told Shima, “Shima, this is the idea how to implement traps. Put traps, you know, figure out how to do the worst possible traps that you can imagine,” and then Shima with his mind, that was steel mind, was able to actually figure out a bunch of traps that he could talk about. > Slater: You want to tell us a little about that Shima? > Shima: I didn’t count [on] talking about that mostly. I placed six traps for stopping the copy of the layout by the copy maker. And one transistor was added to existing enhancement transistors. And I added a transistor looks like an enhancement transistor. But if transistors are set to be always on state by the ion implantations, it has a drastic effect on very much. I heard from NEC later the copy maker delayed the announcement of Z80 compatible product for about six months. > Ungermann: I’m going to go back over a couple of things that we’ve mentioned briefly. But I’ll never forget Shima-san’s ability to take a logic equation and convert it to physical layout of a mask. And I remember many meetings when we were working on the instruction set. And Federico would say, “It really needs this one,” and Shima would say, “No! It adds two more microns.” He would completely analyze the instruction set in real time, and veto or approve the instructions based on his ability to perceive a different world than I work in. > Faggin: Yeah, you remind me of that. Basically, the worst nightmare of when you do layout is at the end you cannot fit everything on this chip size that you have staked for yourself. And toward the end of it, as I was turning the last corner of the chip and finishing, it was very clear that there were too many transistors, and I couldn’t fit them. I had to really compact it more. So it was a very sinking feeling. I pondered for about half-an-hour, and it was obvious that I couldn’t fit it! And so I took an eraser, and I erased three weeks of my work, or two weeks of my work. And I start all over again, and did it, and at the end, I think I had no more than a couple mils left of space at the end. I had forgotten about that, but that was an incredible experience. http://archive.computerhistory.org/resources/text/Oral_History/Zilog_Z80/102658073.05.01.pdf http://archive.computerhistory.org/resources/text/Oral_Histo...