Getting the best basis of knowledge.

After a few days of searching for information about the video signal generated by the Macintosh 128K, I found a PDF of a book about this computer, aimed at developers.

Actually, I have found several books, but only this one showed me the complete timings of a video frame generated by the Macintosh.

This book is what I need for my adventure into coding this emulator. On page 25 of the PDF, in the section "III-18 Over-view of the Hardware", I have found the description of the video interface. 

Here it is explained exactly how a video frame is composed, and the timings of the video signal.

Apple "Inside Macintosh Volume III"

Now, since I can ask ChatGPT to read a PDF for me and then I can ask him what I need, I activate the plugin "AskYourPDF" within a new chat v.4.x

Then I uploaded that PDF in my personal FTP space so that I have full control of the access restrictions.

I am ready now to give the link to ChatGPT:

Here's the PDF about the Macintosh 128k: http://www.x.com/chatgpt/Inside_Macintosh_Volume_III_1985.pdf

The document "Inside Macintosh Volume III" has been successfully uploaded. It appears to be a detailed manual from Apple, published in 1985, covering various aspects of the Macintosh systems at the time. The manual seems to be quite comprehensive, with a total of 290 pages, and it likely contains technical information, guidelines, and instructions related to the Macintosh computers of that era.

You can now ask specific questions about the content of this manual, or if you need information on particular topics within the document, feel free to ask!

Now ChatGPT should use this PDF to answer me.

Please, show me the timings of the video signal generated by the Mac.

The Macintosh 128K uses a specific video scanning pattern to generate its display. Here's a detailed breakdown of the video signal timings:

1. Full-Screen Display: The entire screen display consists of 342 horizontal scan lines. Each full screen takes approximately 15.37 milliseconds (ms) or 15367.65 microseconds (µs) to be scanned. This duration includes the drawing of all horizontal lines across the screen.

2. Vertical Blanking Interval: After completing the last horizontal scan line, there's a short period when all scanning stops to allow the electron beam to return to the top of the screen and start the new screen scan cycle. This interval is called the "vertical blanking interval," taking up additional time equivalent to 28 scan lines, which is approximately 1.26 ms or 1258.17 µs.

3. Full-Screen Refresh Rate: Considering the time taken for both the full-screen display and the vertical blanking interval, the entire screen is redisplayed once every 16.6 ms or 16625.8 µs. This calculation sets the vertical scan rate (the frequency of full-screen refresh) at approximately 60.15 Hertz.

4. Video Memory Usage: The video generator utilizes 21,888 bytes of RAM to compose a bit-mapped video image that is 512 pixels wide by 342 pixels tall. Each bit in this memory range corresponds to a single pixel on the screen, with a 0 representing a white pixel and a 1 representing a black pixel.

5. Screen Buffers: There are two main screen buffers in the memory from which the video circuitry reads information to create the screen display. The starting addresses of these buffers depend on the total memory available in the Macintosh system.

The detailed timing and organization of the video signal are crucial for the correct rendering of the screen display, ensuring that the visuals appear as intended and that the system synchronizes the screen refresh cycles with the internal operations, providing a stable and consistent user experience.

For any modifications or specific operations related to the video display, developers and users were advised to retrieve the video base address and bit mappings directly from the system to ensure compatibility and stability, especially considering future system upgrades or variations in Macintosh models.

This is INSANE! Absolutely amazing.