Gregory's ServerWhy is the die photo distorted at the edges? Because I took the photo through the chip's round quartz window. In the olden days before flash, you could store code in an EPROM, memory that could be erased by exposing it to strong ultraviolet light. The quartz window lets the light in. 2/7
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 @darkling The quick explanation is that an EPROM has a transistor with a"floating" gate for each bit. You program a bit by forcing electrons through the insulating oxide with high voltage, and the electrons are trapped there. Ultraviolet causes ionization in the oxide, releasing the electrons and erasing the chip.  @kenshirriff Thanks! So the programming voltage is applied across the gate and drain, and is sufficient to temporarily break down the resistance of the oxide? Then the surplus electrons sit in the depletion layer, making it not depleted any more, and allow current to flow between source and drain? @darkling Yes, there's a diagram at Wikipedia: https://en.wikipedia.org/wiki/EPROM#Operation  @neffo @darkling Yes, although gamma rays will mess up most chips. The Intel 2920 was designed for a wide range of analog applications from filters to speech synthesis to missile guidance. It was created by Ted Hoff (one of the inventors of the microprocessor) and Marshall Townsend. Although the chip was called "Product of the Year" by the magazine Electronic Products, it was buggy and not a market success. 3/7 Interesting chip art on the Intel 2920: a cactus on the die, maybe because Intel opened a site in Arizona that year. 4/7 The 2920 had four analog inputs and eight analog outputs. The digital-to-analog converter (DAC) was unusual and large: a chain of 256 tiny resistors arranged in a grid. Energizing two digital switches (i.e. transistors) provided a tap for the desired voltage. Analog-to-digital conversion was built on top of the DAC, "guessing" one bit at a time. 5/7 The chip didn't have multiplication or division in hardware, but it had a barrel shifter to quickly multiply or divide by a power of 2. The compiler for the chip is very unusual. Instead of normal code, you define poles and zeros and the compiler builds the code to implement the desired filter. 6/7 Thanks to @tubetime for providing the chip.  @kenshirriff "And you try and tell the young people of today that ... they won't believe you."  More than 40 years ago, I used the UV facial tanner lamp of my mom to erase the UV EPROMs I put into my ZX Spectrum. Fun times! |
@kenshirriff There's something I never realised I didn't know: how does an EPROM actually work at the component level? (And is it related to the thing about not being able to take flash photos of an uncased Raspberry Pi without it crashing?)