The 2920 had four analog inputs and eight analog outputs....

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.

Like 2 September at 16:34 | Open on oldbytes.space

2 comments

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

Ken Shirriff

Thanks to @tubetime for providing the chip.
References:
An evaluation by JPL summarizing the chip's problems: https://ipnpr.jpl.nasa.gov/progress_report/42-63/63O.PDF
Patent on the chip: https://patents.google.com/patent/US4319325A
Documents: http://www.bitsavers.org/components/intel/2920
Datasheet: https://archive.org/details/2920-16-signal-processor
Article: https://www.worldradiohistory.com/Archive-Electronics/70s/79/Electronics-1979-03-01.pdf#page=105
7/7

Part of a two-page ad for the Intel 2920. This page shows an illustrated man standing in front of microphones with the label "Intel Special Report."

Second page of advertising for the 2920 chip, a full page of text. It is titled "LSI Breakthrough for Analog. Intel announces the 2920 Signal Processor, first general purpose, real-time system on a chip."
From Electronics, Jan 31, 1980.

2 September at 16:40 | Open on oldbytes.space

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