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Ken Shirriff

Interesting chip art on the Intel 2920: a cactus on the die, maybe because Intel opened a site in Arizona that year. 4/7

Closeup of the die showing copyright intel 1981, along with a saguaro cactus.
2 September at 16:32 | Open on oldbytes.space
3 comments
Ken Shirriff

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

Closeup of the die showing the square grid that forms the digital to analog converter.
2 September at 16:34 | Open on oldbytes.space
Ken Shirriff

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

A diagram from the manual for the SPAC20 Compiler showing how poles are specified and then the compiler displays the filter response using ASCII art.
2 September at 16:35 | Open on oldbytes.space
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