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VONO, from 6
terestingly, the tape recorder needed to be a cheap
one with few filters since the digital data was re-
corded in the bandwidth of the noise.
The D37C, on the other hand, kept its data on a
rotating disk. However, the read and write heads
were “nailed down” so the programmer had to
know when the data was near the read or the write
head. Programming occurred using “word times.”
Assembly language was a convenience, a step
up from machine language which programs the
Z80 chip directly in its own internal code. But
the TRS80 was so small, I needed to resort to
machine language to get certain efficiencies. This
hobby got me “speaking chip” more fluently. I got
comfortable with using storage registers, that is,
where to put data and where to put instructions as
an example. How to do binary math using “twos
complement.”
Using the Z80 instruction set, I could load data
and computer programs into the TRS-80 memory.
The registers and wiring on the chip helped that Figure 5: NAND Gate Logic (graphic by author)
process.
It wasn’t a big stretch. My degree at the Acad-
emy was in Astronautical Engineering. But to started studying. Logical Description,” provides hundreds of pages gear in the Minuteman III, including the D37D
compute those orbits and their perturbations, we On one end, it had 33 cards, mostly filled with of the NAND gate connectivity needed to do, for computers, were modernized (i.e. replaced) in
needed to be in the computer room most of the NAND gates. (See figure 5.) I learned that we instance, twos complement math. And don’t get 1999. A design challenge was to ensure the new
time. In fact, the department was “The Department practically owned Texas Instrument’s chip produc- me started on their wiring diagrams!! I’ll ensure computer could be just as “hard” to nuclear bomb
of Astronautics and Computer Science.” I took a tion line back in the 1960s as these were being a damper on any raucous party. radiation as the older version.
lot of extra classes from the computer science pro- built. On the other end was a spinning disk with I learned that chips that didn’t go into Minute- Now you know a tiny bit more of Cold War
fessors, since I was interested in that area. Before fixed read and write heads. As mentioned before, man II made their way into the Apollo Moon Shot. history and the rise of the personal/office/home
I got my appointment to the Air Force Academy, the software had to operate in “word times” to So, ICBM engineers would often refer to “Apollo- computer.
I was signed up for CalPoly San Luis Obispo in ensure read and write operations occurred when era electronics” when discussing our Minuteman Just remember, EX DE, HL Swaps H with D
a brand-new field called “Computer Science.” At the heads were lined up with the data. electronics, even when discussing the more mod- and L with E.
CalPoly, it was in their math department. OK. My “aha!” moment was when I realized that ern Minuteman III.
Maybe I am ancient. all those machine language instructions, the Z80 The Minuteman III ICBM sported the new and Editor’s note: Charlie Vono is a retired U.S. Air
When I left active duty Air Force and started instruction set I had learned for the tiny Z80 chip, improved D37D computer, which was an upgrade Force colonel and retired defense contractor born
work at TRW in 1985, I was told to “become an had their equivalents in those dozens and dozens of the D37C, but essentially the same. Minute- and raised in Wasco, Calif., and currently living in
expert” in the Minuteman II D37C. And so, I of NAND gates spread across the bulk of the 33 man II was retired in the 1990s; the last silo was Ogden Utah. See charlesvono.com for his videos
gathered up all the technical manuals I could and modules. For instance, Boeing’s book, “D37C imploded in 1997. All of the guidance electronic on various aerospace subjects.

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