Image Map Image Map
Page 2 of 2 FirstFirst 12
Results 11 to 20 of 20

Thread: Apple IIGS with Turbo->28 boot screen

  1. #11
    Join Date
    Jan 2014
    Location
    Freedom City
    Posts
    6,160
    Blog Entries
    2

    Default

    Saying the ||GS is just a //e with other things tacked on isn't exactly right, in my opinion. It's really a whole different machine with a //e tacked on.

    Granted most people only used them as a fast //e. At least that's what I saw in the early days. I don't think I ever saw one with a ROM3.

  2. #12

    Default

    Quote Originally Posted by KC9UDX View Post
    Saying the ||GS is just a //e with other things tacked on isn't exactly right, in my opinion. It's really a whole different machine with a //e tacked on.
    It isn't that much of a different machine. You can remove the FPI/CYA and put a 6502 CPU directly onto the MEGA2 Chip. It would function as a Apple iie with a fancy graphics- and sound card. The GS is a true Apple II.

    The funny thing ist that the Apple IIe graphics modes are still generated by the mega II and are fed to the VGC via a 4bit data stream. The VGC converts this into the video output. You can grab the original Apple II video (1bit data stream) from the Meag2 and add composite sync to get the original Apple IIe NTSC The VGC generates its own video modes that are fed through the memory refresh cycle. The funny thing is that the VGC is 'hardwired' to a fixed bank of 64k of the slow memory (//e side). This is the reason why the IIgs has only a single video page.

    If you look into the shematics, you can easily see the separate parts of the IIgs. The CPU and fastmem are a separate entity from the rest of the system. The IIgs is a fancy //e with a built-in accelerator. It is maybe more close related to the //c if you look at all the pre-installed hardware. The IIgs is very different from a programming perspective, though. There are a lot of softswitches and registers present in the IIgs that are unique to this machine. The FPI/CYA maps several functions of the slow part of the computer into the fast part in a very efficient way. Some parts of the slow-mem are mapped into the fast-mem and even the floppy can be accessed without slowing down the cpu, even though the floppy is on the 1mhz part of the computer... Apple did a good job to integrate the old system with the new CPU. But this method of designing the IIgs has led to the problem, that the graphics access is actually very slow. The typical read-modify-write cycle is much slower than if the VGC were located in the fast part of the Igs

    -Jonas

  3. #13
    Join Date
    Aug 2006
    Location
    Chicagoland, Illinois, USA
    Posts
    5,418
    Blog Entries
    1

    Default

    Any ideas as to why Apple did that for the system? Was it for 100% Apple II compatibility? Tying the IIgs's video RAM to fastram would have made the IIgs more pleasant for action gaming had they done so.

    Wait, didn't they map the Ensoniq to 64K as well? IMO that really hobbled what you could do with the chip, and it's not like they had any Apple II compatibility to worry about...
    Offering a bounty for:
    - The software "Overhead Express" (doesn't have to be original, can be a copy)
    - A working Sanyo MBC-775, Olivetti M24, or Logabax 1600
    - Documentation and original disks for: Panasonic Sr. Partner, Zenith Z-160 series
    - Music Construction Set, IBM Music Feature edition (has red sticker on front stating IBM Music Feature)

  4. #14

    Default

    Probably a rom made during the development of the ROM 4 Twain which never went to market. Notice the similarity in the top header of the rom 04 source code which I assembled about 5 years ago.
    https://www.callapple.org/vintage-ap...totype-rom-03/
    Hey, by any chance does that //gs have a 1.44MB superdrive 3.5 floppy?

    Larry G

  5. #15

    Default

    Quote Originally Posted by retrogear View Post
    Probably a rom made during the development of the ROM 4 Twain which never went to market. Notice the similarity in the top header of the rom 04 source code which I assembled about 5 years ago.
    https://www.callapple.org/vintage-ap...totype-rom-03/

    Larry G
    @retrogear: Very interesting
    The 28 of the turbo ->28 could be the release number... -> Apple IIgs 'turbo' ROM release 28 maybe the ROM03 is actually ROM release 30 ?

    @Trixter: I don't understand the thought process behind these decisions at apple myself. Maybe the IIgs was derived from bits and pieces Apple had already developed for the never released Apple IIx?

    But I would suspect that the IIgs was designed to be able to access all the added functionality even in 8bit 6502 emulation mode since very few developers could actually program 65816 code at the release of the IIgs. This would allow software written for the //e to access all the added functionality of the IIgs without breaking the 64k boundary. You could use all the available development software for the A2 with the IIgs without modifications. But maybe a IIgs compatible graphics solution for the //e was planned (there was the Video Overlay Card in 1988 ) and maybe even an ensoniq sound card? Apple was always very secretive about these kind of decisions...

    -Jonas

  6. #16
    Join Date
    Jan 2014
    Location
    Freedom City
    Posts
    6,160
    Blog Entries
    2

    Default

    Also one of the design goals of the GS was to make sure it didn't outshine the Mac.

  7. #17

    Default

    Quote Originally Posted by Trixter View Post
    Any ideas as to why Apple did that for the system? Was it for 100% Apple II compatibility? Tying the IIgs's video RAM to fastram would have made the IIgs more pleasant for action gaming had they done so.

    Wait, didn't they map the Ensoniq to 64K as well? IMO that really hobbled what you could do with the chip, and it's not like they had any Apple II compatibility to worry about...
    The Ensoniq DOC's RAM was never directly addressable, everything with that chip is done via the Sound GLU chip. Don't know why the VGC's RAM was mapped to slow RAM. I guess it was to keep fast RAM completely free for 16-bit applications (remember this machine shipped with only 128k fast memory and 128k slow memory). There are some speed up tricks one can do with shadowing the VGC's RAM, but it can only do so much. The whole RAM shadowing thing was to keep onboard fast RAM contiguous with any expansion RAM, but allow timing sensitive 8-bit software to still run in the slow RAM and expect it at page 0 and 1.

  8. #18

    Default

    If you could capture the turbo 28 ROM bin for study, I would appreciate it.
    There is a gsos app that captures the rom. I've used it in the past, works well. Search for "grabber" in here:
    ftp://ftp.apple.asimov.net/pub/apple...rs/rom_images/

    Larry G

  9. Default

    I took some pictures of the unit. It is a ROM3 board with two hand-made ROMs, housed in a Woz limited case but without the label at the bottom. Most of the IC datecodes are 883X, and the latest is 8911. Will this just a hobbyist unit built with parts from multiple sources? or a developer unit?


    IMG_0242.jpgIMG_0239.jpgIMG_0237.jpgIMG_0236.jpgIMG_0238.jpg
    Mac IIFX with MicroExplorer

  10. #20
    Join Date
    Mar 2012
    Location
    Augusta, Georgia, USA
    Posts
    453

    Default

    Quote Originally Posted by michaelsw View Post
    I took some pictures of the unit. It is a ROM3 board with two hand-made ROMs, housed in a Woz limited case but without the label at the bottom. Most of the IC datecodes are 883X, and the latest is 8911. Will this just a hobbyist unit built with parts from multiple sources? or a developer unit?


    IMG_0242.jpgIMG_0239.jpgIMG_0237.jpgIMG_0236.jpgIMG_0238.jpg
    Likely an internal prototype or Apple employee machine...

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •