History: logic you program

1947 — the transistor. At Bell Labs John Bardeen and Walter Brattain pressed two gold strips against a piece of germanium — and a weak current through one strip began to control a strong current through the other. William Shockley soon came up with a transistor that was easier to make. In 1956 all three received the Nobel Prize in Physics. All our kits are built from transistors — their descendants.

germaniumplasticemittercollectortwo gold strips almost touchingbase1947Bell LabsBardeen, Brattain,Shockley1956 — Nobel Prizein Physics
The first transistor — a point-contact one: a piece of germanium and two gold strips on a plastic wedge. A weak current through one strip controlled a strong current through the other.

First — a board of chips. For a long time logic was built from ready chips: dozens of 74-series packages on a board, and the circuit was the way the tracks ran between them. Want another circuit — make a new board. When many devices were needed, the circuit went to a factory that made a custom chip: cheap in large runs, but every mistake meant new months and new money.

a board of chipscircuit = wiresa custom chipcircuit = factory×××××××PALburn onceGALprogram and eraseFPGAmillions of fusesthis kit
Where the circuit lives. First — in the wires between chips, then — at the factory that makes a custom chip. The PAL put the circuit in the engineer’s hands, but only once; the GAL — as many times as you like; the FPGA can be reprogrammed too, but holds thousands of blocks — a whole processor fits inside.

1967 — the floating gate. At Bell Labs Dawon Kahng and Simon Sze came up with a transistor whose gate is connected to nothing: a charge on it stays for years. It is a transistor that remembers.

1971 — the Intel 1702. Dov Frohman used such transistors to make the first ROM that could be erased and written again — a 2,048-bit EPROM. It was erased with ultraviolet light through a quartz window in the package. A few years later EPROMs were in almost every computer: they held start-up programs and fonts.

floating gate1967Bell Labs:a transistor remembersIntel 17021971EPROM,erased by UV lightPAL1978fusesare burntGAL1985fuses aretransistorsFPGAtodaymillionsof fusesthe .jed firmware format has stayed the same since the 1980s
From a transistor that remembers to chips that are programmed with a file.

1978 — the PAL. At MMI John Birkner and H. T. Chua made a programmable AND-OR matrix with fuses that are burnt by a current. An engineer wrote equations, the PALASM program turned them into a fuse map, and a programmer burnt the unneeded ones. One PAL replaced a dozen 74-series chips on a board. But a mistake in an equation meant throwing the chip away.

1985 — the GAL. Lattice Semiconductor replaced the burnt fuses with floating-gate transistors that are erased electrically. The GAL22V10 could do everything the various PALs could — the macrocell on every output is set by two bits. Made a mistake — erase and program again, in seconds.

JEDEC. So that any programmer could write the firmware from any program, a file format was agreed on: text listing all the fuses in order, 0 or 1, and a checksum. These are the .jed files. Equation programs — PALASM, ABEL, CUPL, later the free galasm — all write the same format.

Today. In 2010 Lattice discontinued the GAL22V10: FPGAs took its place. But the compatible ATF22V10C (made by Atmel, now Microchip) is still in production: the same pins, the same .jed files. People use it to repair old computers and arcade machines where PALs once sat. And the idea of "logic you program with a file" grew into the FPGA: it can also be reprogrammed any number of times, but inside there is not one matrix for 10 outputs but thousands of small blocks — a whole processor fits into one FPGA.