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I'm interested in the design of the VIC, the video and sound chip in the Vic-20. (Not too be confused with the VIC-II, which has been discussed elsewhere on the site.) I haven't been able to find an annotated die photo. I have found three good though unannotated ones at http://www.vic20.de/html/vic_6560-6561.html

As a reminder, to quote Wikipedia,

Its features include:

  • 16 kB address space for screen, character and color memory (only 5 kB points to RAM on the VIC-20 without a hardware modification)
  • 16 colors (the upper 8 can only be used in the global background and auxiliary colors)
  • two selectable character sizes (8×8 or 8×16 bits; the pixel width is 1 bit for "hires" characters and 2 bits for "multicolor" characters)
  • maximum video resolution depends on the television system (176 × 184 is the standard for the VIC-20 firmware, although up to 248 × 232p/464i is possible on the NTSC machine and up to 256 × 280 is possible on the PAL machine[1])
  • 4 channel sound system (3 square wave + "white" noise + global volume setting)
  • on-chip DMA
  • two 8-bit analog-to-digital converter
  • light pen support

What can we identify as being implemented in which part of the above die photos?

In the top left, there is a column of four complex structures, that look identical. I would hazard to guess those are the four voices of sound?

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    Here's an experiment: Take the wikipedia description of some chip that has been reverse engineered, have a look at the die shot, and try to "guess" which part is which. Chances are at least 50:50 that you'll guess wrong for quite a few parts. So there's no way around actually reverse engineering this thing. E.g. start with the pins, and see where they connect. Commented May 27, 2024 at 14:01
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    BTW: Someone seems to be reverse engineering it right now, metal layer with labelled pins. Commented May 27, 2024 at 17:34
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    If memory serves, it's also a known weird implementation in places, just from externally-observable behaviour; e.g. the square wave audio is actually an 8-bit LFSR with a single tap point and enable/disable just masks the bit being fed back into the start. So you can force in any 8-bit pattern by careful timing of enable/disable and it'll loop around indefinitely, alternating with its complement. Commented May 28, 2024 at 14:37

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