Wednesday, May 23, 2012

Intel 486DX (80486)



The Intel 80486, more commonly known as an i486, added on chip cache and an FPU over the 80386.  The caches are easily visible as the black areas to the left.  I'm not sure which of the random logic areas are the FPU, maybe a comparison with a 386 would make it obvious.  I assumed there was no 80487, but it looks like there is abeit used in a creative upgrade path where you don't need your CPU anymore.

Intel logo:

And designer initials:

Roughly 70 people working on the chip.  It looks like some have 3 initials to clarify duplicates, but it does make me wonder how it was decided how represented the 2 initial versions.  Also unclear of grouping, is not alphabetical by first or last name.

I was also a bit surprised to see the mask ROM at the bottom.  Maybe microcode?  I don't think Intel microcode could be updated until later but would make sense that it was still easier to design with hard coded microcode.

The die shot also looks similar to the 80486DX2 picture on Wikipedia (CC-BY-SA Matt Britt / Matt Gibbs):

While things are in the same general place it looks like there were some layout changes between the two as components are roughly the same size but look to be laid out a little different.  It also could be a difference between epi and inspection scope illumination.

One interesting thing I found from on the Wikipedia page: "Although the 486 became obsolete for personal computer applications by the mid-1990s, Intel had continued production for use in embedded systems. In May 2006 Intel announced that production of the 80486 would stop at the end of September 2007." Things do stick around longer than you intend.

I have a 20x objective scan (this is 5x objective w/ 10x relay lens for 50x total) where you can actually see all the wires, will try to stitch and post.

Sunday, May 6, 2012



Okay, so its really a 1702A, but the datasheet says they are the same die and that's what the die is marked.  With a 1973 die copyright this could be one of the oldest pieces of silicon I have.  Not exactly ightning fast by today's standard, but boasts a "fast programming time" of 2048 bits in 2 minutes ie slightly over 17 bits per seconds or about half a second to burn in each byte.