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Thread: Is the "AppleColor High-Resolution RGB Monitor" usable with the Laser 128 system?

  1. #11
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    Quote Originally Posted by misterblack View Post
    Sounds like the laser may have TTL RGB or it may not. Either way, this would be a 15khz refresh rate but it is probably more like the Apple III color mapping than anything else -- so not the same as a CGA monitor (if you could make the adapter.) Laser may have sold a specific monitor for this machine -- or you'll need to investigate with oscilloscope if digital RGB signals are avail and what the sync signals look like. A CGA type monitor may work if the sync is right, but almost certainly the colors will be wrong. CGA does not have the same 16 colors as an Apple II.
    I'm not quite sure how the "color mapping" is going to be different on an Apple III; the pinout in the Apple III service manual is indeed remarkably vague about what "RGB1" through "RGB8" map to, but cross-referencing that against this article about adapting an Apple II RGB card that appears to have the same pinout to drive an analog monitor it has the same "RGBI" color space as CGA. (The one thing that may well be different is monitors specifically targeting the Apple II/III might not have the "Brown Fix" circuitry that turns "dark yellow" into the nicer brown that's standard on CGA.) The color set possible with 4 bit RGBI certainly is going to be different from the NTSC-tweaky colors you get over the composite port in an Apple II; granted I've never seen an RGB-equipped Apple II or III in the flesh but my guess is the displayed colors simply don't match the composite colors particularly closely. If someone has a working Apple II RGB setup I'd be curious to see some side-by-side shots.

    (They don't quite match up on the IIgs, either, despite that machine having a 12 bit palette to choose from for the lookup table it uses when faking composite color over the RGB port.)

    Regarding actual CGA monitor compatibility in particular, well, that's another story. The Apple II/III TTL RGB ports apparently used composite sync, which would definitely be an issue for most real CGA monitors. The pinout for the Laser 128 in the Apple II FAQ, however, indicates it has both a /CSYNC line and separate HSYNC/VSYNC lines:

    Laser 128

    This was an Apple //c clone. But its video port differs from the //c. While
    I believe it may work with the //c LCD display and with adapter cables that
    split out composite video and sound, it also has the signals needed for an
    RGB display without any extra circuitry.

    Laser 128

    1. INTEN
    2. F14M
    3. RED
    4. BLUE
    5. SOUND
    6. LDPS
    7. DSPEN
    8. +12v
    9. HSYNC
    10. /CSYNC
    11. CGSEROUT
    12. NTSC (Composite video)
    13. Ground
    14. VSYNC
    15. GREEN
    IF that pinout is accurate then it looks like they intended it to be able to drive either an AppleColor 100-type monitor or a CGA monitor depending on what cable you use. In any case, it looks like it's basically not compatible with ANY monitor using a plain off-the-shelf straight-through 15 pin cable.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  2. #12
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    Quote Originally Posted by Eudimorphodon View Post
    Regarding actual CGA monitor compatibility in particular, well, that's another story. The Apple II/III TTL RGB ports apparently used composite sync, which would definitely be an issue for most real CGA monitors.
    For interest's sake here's a schematic for turning the Apple II/III TTL RGB CSYNC into separate syncs for a CGA monitor, although it cuts a few corners that some monitors might not put up with.
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  3. #13
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    Quote Originally Posted by misterblack View Post
    Apple used that same DB15 on many computers and monitors and they are very much not interchangable.
    Also beware of Apple's reuse of that DB19 they used for floppy drives; there are a number of mutually incompatible implementations of that as well. Some combinations simply won't work, others will nuke your floppy controller. (It's mostly Macs that suffer the nuke scenarios.)
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  4. #14

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    Quote Originally Posted by misterblack View Post
    Apple used that same DB15 on many computers and monitors and they are very much not interchangable.

    IIgs -> 15khz analog RGB w/ composite sync
    IIc/IIc+ -> no RGB signals at all, has memory bitstream output that requires external hardware to convert to RGB (or drive the LCD monitor) -- has composite video but also has 12v so can easily damage things plugged into it
    Macingoth DB15 video port -> Analog RGB with H+V sync (not sure on the sync) but the signals run at north of 31khz (VGA)
    Apple III -> has a DB15 port too and this one is TTL RGB but doesn't use the same color mapping as CGA/Commodore 128 so finding a monitor that works with this isn't easy anymore. Pin out may be different.

    So a Mac monitor and IIgs monitor are NOT interchangeable even with the same connekor. And you should not plug either monitor into IIc/IIc+ or Apple III ever.

    Sounds like the laser may have TTL RGB or it may not. Either way, this would be a 15khz refresh rate but it is probably more like the Apple III color mapping than anything else -- so not the same as a CGA monitor (if you could make the adapter.) Laser may have sold a specific monitor for this machine -- or you'll need to investigate with oscilloscope if digital RGB signals are avail and what the sync signals look like. A CGA type monitor may work if the sync is right, but almost certainly the colors will be wrong. CGA does not have the same 16 colors as an Apple II.
    Many CGA monitors if fed with Apple2's composite sync on both their VSYNC & HSYNC inputs work nicely (DMC for example). Even the AE ColorLink does not produce NTSC colors on a CGA monitor. Even the original Apple //GS color RGB monitor shows different colors than NTSC. There are very few designs that do mimic NTSC via PWM of the RGB's CGA TTL signals. I do think that Laser's RGB output is meant for CGA/EGA monitor direct usage. The colors may differ slightly from NTSC but that's by design.

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