Path: csiph.com!weretis.net!feeder8.news.weretis.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: D Finnigan Newsgroups: comp.sys.apple2 Subject: Re: How does the Apple IIGS emulate a =?UTF-8?B?SUllPw==?= Date: Fri, 16 Feb 2024 13:59:46 -0000 (UTC) Organization: Mac GUI Lines: 42 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Fri, 16 Feb 2024 13:59:46 -0000 (UTC) Injection-Info: dont-email.me; posting-host="07bb8ea85ec512f6f9357055442e8f8b"; logging-data="4081650"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19IZLKmkYf8yMLo/DLb3QSw" User-Agent: Mac GUI Usenet Cancel-Lock: sha1:uLNhoNkeiiJECO1aCrcWshTBEKg= In-Reply-To: Xref: csiph.com comp.sys.apple2:48859 Kelvin Sherlock wrote: > --- > It's possible that everybody, including Apple, has been wrong for 37 > years but extraordinary claims require extraordinary evidence. > I found articles going back to the 1986 release of the IIgs that described the Mega II as a "complete Apple II on a chip." Most likely someone made an assumption about the chip, and it spread around, was repeated, and stuck for 37 years. This happens in every knowledge domain, not just with vintage computers. Here's a post from September 1986 that asks if the Mega II is an emulator chip: https://macgui.com/usenet/?group=6&id=3010 Here's a reference to an October 1986 BYTE Magazine article about the Mega II: https://macgui.com/usenet/?group=1&id=3626 THE MEGA II The Mega II is a custom CMOS chip containing about 3000 gates and a 2K-byte by 8 ROM (for the character generator). It replaces the following chips from the Apple IIe and IIe: char­acter generator ROMs for eight lan­guages. several TTL chips that per­form logic functions. and the MMU (memory management unit). IOU (in­put/output unit). TMG (timing genera­tor). and GLU (general logic unit) custom chips. In previous Apple II designs, the re­freshing of memory was tied directly to the Apple II video mode. The Mega II includes an 8-bit counter for refresh­ing the 128K bytes of (slow) memory associated with the Apple IIe/IIc model; it does five cycles of RAM refresh during the horizontal retrace of each video scan line and refreshes the 128K bytes of memory in 3.25 milliseconds. By taking care of RAM refresh the Mega II chip opens the Apple II design to new video modes that were impossible before. -- ]DF$ The New Apple II User's Guide: https://macgui.com/newa2guide/