I was reading about the Audio/Video port pinouts of the VIC-20 and I noticed that pin 4 is VID L and pin 5 is VID H meaning Video Low and Video High, respectively.

I'm familiar with luma, chroma, etc. but the term Video Low and Video High confuses me in the context of the VIC-20.

Can anyone shed some light on this subject?


1 Answer 1


The VLOW signal on Pin 4 of the VIC-20's monitor port has a low-pass filter applied to it, where Pin 5 (VHIGH) is not filtered. See this post, which specifically says:

Then the signal is buffered by emitter follower Q7, with a 270 ohm load and fed to pin 5 of the video socket directly and to pin 4 via 3.9uH inductor L2 and C18 which together form a low pass filter. I need to confirm the value of C18 from a real machine, the marking is hard to make out on the scanned copy, but I would expect the cutoff frequency to be of the order of 5MHz.

  • 1
    Per retroisle.com/commodore/vic20/Technical/Hardware/VIC20ports.php some revisions of the machine don't include the low-pass filter and just put the same thing on both pins. The thread you link to mentions that the cost-reduced Vic-20 varied from its own schematic in combining luminance and chrominance; if the Retro Isle information is correct then I guess Commodore decided to reduce costs even further?
    – Tommy
    May 22, 2017 at 16:08

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