You can freely build on How Wozniak Made the Apple II Display Color Graphics

What this patent covers

This patent describes a timing circuit that synchronizes a computer's digital signals with the analog signal requirements of a standard television. Because televisions use a specific color frequency (the color subcarrier), simply outputting digital data often resulted in blurry or 'crawling' colors. Wozniak's invention uses a horizontal synchronization counter that is locked to an odd-submultiple of the color frequency. By introducing a specific 'delayed' count into this cycle, the system ensures that the color phase remains consistent across different scan lines, preventing the color distortion that would otherwise occur on a consumer CRT display.

What is now free to use

All 1 claims of US 4136359 are in the public domain. Specifically:

• Claim 1: In a microcomputer for use with a video display an improved timing apparatus — 7 specific elements

The 0 dependent claims add narrowing limitations and are also free.

What is NOT covered

Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.

• Does not cover non-raster scan display technologies like modern LCD or OLED panels.

• Does not cover software-based color generation methods that do not rely on hardware-level timing synchronization.

• Does not cover high-definition (HD) or 4K signal timing protocols.

• Does not cover the specific logic used to store the pixel data itself, only the timing synchronization for the output.

Who is building on this today

While this specific hardware approach is largely obsolete due to digital display standards, the legacy of this design lives on in the engineering philosophy of Apple. Modern companies like NVIDIA and AMD continue to solve similar synchronization challenges, though they now manage them through complex GPU driver stacks and high-speed digital interfaces like DisplayPort rather than discrete timing counters.

Products built on expired version of this technology

How to cite this patent in your documentation

Apple Computer Inc. US Patent 4136359. Microcomputer for use with video display. Granted 1979, expired 1997. Now in the public domain.

Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.

PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.