But the borders were thick even when I had the 68.4V VGA Mod and used my LC575 Board with the IIe Card...
@JDW,
That's interesting. I assumed that a CC stock board to behave the same as a Mac TV/520/550/575 board in terms of standard Mac video timing (and thus geometry) at 640x480 67Hz. But now you've got me thinking.
First, some basics:
- The CC (and Mac TV)'s video comes from the Spice and Tinker Bell ASICs, which are evolutions of the V8 gate array from the LC / LC II. These ASICs handle video generation, and they're descendants of the RAM-Based video used in the IIci.
- The LC III replaced V8 with Sonora, which improved its video generation capabilities considerably. The Sonora was then refined into the Ardberg used in the LC 520/550 logic board.
- The LC, LC II, LC III, CC, LC 520, and LC 550 all use the same Ariel RAMDAC. The Mac TV's Ariel+ is largely the same.
- The LC 575 (and LC 475 / Quadra 605) use MEMCjr and the Antelope RAMDAC to generate video. This is a revision of the djMEMC video from Q800/650/610 which itself is a reimplementation of the Direct Access Frame buffer developed for the Q700/900.
I have a Color Classic and Mac TV with original logic boards. I also have an LC 550 logic board (Color Classic II is identical).
My Color Classic has not been modded for 640x480 output. So I decided to run some tests:
- I booted both the Color Classic and Macintosh TV with their original boards as sanity tests. My machines need some geometry adjustment, but it's good enough for a baseline. The image is largely centered on both.
- I put the Mac TV and LC 550 logic boards into the Color Classic to verify their operation on the 10 inch display (which AFAIK the operating system and sense lines treat like an Apple 12 inch RGB display for the LC machines). The geometry on all three were identical at 512x384 60Hz, as far as I could see.
- I put the Color Classic board in the Macintosh TV and the geometry was identical to the Macintosh TV board. This makes sense, because their video generation circuitry is largely the same.
- I put the LC 550 logic board in the Mac TV and the geometry was different! The display was shifted over to the left by a noticeable amount (about a quarter of an inch). I didn't measure the actual size of the image.
When I was doing research on Mac built-in video and RAMDAC designs recently for "
How Much VRAM Does a Mac Color Classic II Have, Anyway?" I couldn't get a definitive answer on whether Sonora or Andberg's improved video generation was based on efforts done for Direct Access Framebuffer and the djMEMC. The LC III was released at the same time as the Q800/650/610, but because it uses the Ariel RAMDAC can't use resolutions greater than 832x624. The Antelope or AC/DC RAMDAC is needed for higher resolutions. Since you say the LC 550 board behaves the same as an LC 575, I'm inclined to believe that the video circuitry in Sonora/Andberg is in fact related to DABF and similar to what's in djMEMC/MEMCjr.
After going back into the Apple Developer Notes for the IIci, LC, LC III, and LC 520, I discovered something I overlooked when doing that research: the timings for the 640x480 67 Hz mode are different on the LC! The LC III and LC 520 match the IIci with the following specs:
Dot Clock: 30.24 MHz
Dot Time: 33.07 ns
Line Rate: 35.00 KHz
Line Time: 28.57 microseconds
Frame Rate: 66.67 Hz
Frame Time: 15 ms
Here's the diagrams:
IIci:
LC III:
LC 520:
However, the LC / LC II is clearly different. Although there is no Mac TV dev note and the Color Classic doesn't mention 640x480 mode, I have a hunch that their timings match LC / LC II based on what we've observed.
Dot Clock: 31.3344 MHz
Dot Time: 31.91 ns
Line Rate: 34.975 KHz
Line Time: 28.59 microseconds
Frame Rate: 66.62 Hz
Frame Time: 15.01 ms
Based on these timing diagrams the difference in geometry we're seeing when using a Color Classic or Macintosh TV logic board in a Hook chassis versus versus an LC 520/550/575 board makes perfect sense. The horizontal blanking interval on the LC / LC II / Color Classic / MacTV is longer, resulting in the image being shifted over to the right. Conversely, using a LC 520/550/575 board in an 84V modded CC will result in the image being shifted to the left.
A test I would try for sake of curiosity would be to take an AppleColor 13 inch or other monitor that's fixed at 640x480 67 Hz and do the following:
- Hook it up to an LC III and adjust the geometry for a properly sized / positioned display.
- Plug the monitor into a IIci. The geometry should be the same.
- Plug the monitor into an LC 475 / Quadra 605. The geometry should be the same.
- Plug the monitor into an LC / LC II. The geometry should change.
Now, the question is why does the LC / LC II / Color Classic / Mac TV have a longer horizontal blanking at 640 x 480 67Hz versus the rest of the Mac family? That I can't say. My hunch is that it has something to do with the Apple IIe mode when using a 640x480 monitor on an LC / LC II.
Now we're on to the next bit: the quirks of the Apple IIe card's video modes. The computers that are compatible with the card all have slightly different handling of that mode depending on what monitor (or all-in-one) is used.
LC / LC II / LC III / Color Classic / LC 475 / Quadra 605 with 12 inch RGB monitor: special 560x384 60Hz mode. Note: When the IIe card is used in the LC, LC II, and Color Classic the timing signal for this special mode is generated by the IIe card itself and transmitted over pin 31 of the PDS slot. This signal ignored in the LC III and later because the IIe video timing is generated by the Sonora/Andberg/MEMCjr ASICs.
Color Classic / CC II / LC 520 / LC 550 inside a Color Classic: special 560x384 mode (same as 12 inch RGB monitor).
LC 520/550: Apparently the Apple IIe mode on these machines is supposed to switch to an actual 560x384 60 Hz mode. I don't have a IIe card to test this. It won't take up the whole area of the display; it would be a bordered mode (similar to what JDW saw in his video). I'm wondering if this is an error, given how other headless LC machines operate with 640 x 480 67Hz monitors and Apple IIe cards, as we'll see below. But I am curious.
JDW, can you try the combination of LC520 board with Apple IIe card in your VGA modded CC and see what happens? I don't recall seeing you post it here or in the video. I'm curious if it behaves differently than your LC 575 board with Apple IIe card.
LC 575: Unlike the 520, the 575's tech note specifically declares that it uses the standard 640x480 67Hz mode but displays the 560x384 mode in the middle of the display.
LC 475 / Quadra 605 with 67Hz display: The tech notes have this to say:
When the Apple IIe Card for Macintosh is installed in the expansion slot, the computer generates an Apple IIe video display with 560 by 384 pixels. On the 12-inch color monitor, that display requires changes to the video timing, as shown in Table 2-2.
The Macintosh LC 475 and Macintosh Quadra 605 computers can provide a 560-by-384 display on any size monitor; only the 12-inch monitor requires modified timing parameters to provide the 560-pixel display width.
They're identical to the 575, except it seems like it can generate a IIe mode display on any monitor that can be attached.
LC / LC II with 640x480 67Hz display: mg.man
tested this out earlier in this thread and got a 640 x 480 67 Hz display with bordered output. I would be very curious to see how this would match a...
LC III with 640 x 480 67Hz display: I bet the geometry would look slightly different in IIe mode, or the border would be slightly different. You'd still end up with a bordered 67Hz display either way. The Sonora (and presumably Andberg) ASIC does support VGA 60 Hz output, and my hunch is that the 640x480 60Hz mode seen on the LC 520/550 is actually the VGA mode with a border. That said, the real curiosity is...
LC III, LC 475, or Quadra 605 with higher resolution displays: Has anyone tried the IIe card when the resolution is set to 832x624 or higher on an LC III, LC 475, or Quadra 609? Is it just a smaller display in the middle with progressively larger borders?
I really enjoyed your video. I am currently gathering the components to also do the 84v mod. I wonder if a ROM hack would be able to give the option for the different resolutions.
The problem with enabling the hidden 560x384 mode for a Mac desktop on the Color Classic is that the geometry will be wrong when you change resolutions. It would end up squished horizontally with the standard geometry. That works for IIe mode because the IIe display has rectangular pixels! For proper square pixels you'd end up needing to adjust the H/V size to square things up and you'd end up with black borders on the top and bottom of the display.. You can't adjust the H / V size without removing the back of the case, so... That's likely why it's locked out as a selectable resolution. The technotes I've seen also say this mode is limited to 4-bit color. The Quadra 605 / LC 475 tech note says this mode can be explicitly chosen in the monitors control panel on a multisync or 12-inch RGB monitor, but I don't have one around to verify.
And very sadly, on top of that, the monitor is NOT multi-sync, which is why you are then forced to do the CRT Adjustments via the POTs at back (requiring the rear plastic housing to be removed). Meaning, you are forced to change the sense lines to switch between the stock resolution and VGA, and then you must change the CRT adjustment POTs to get the video centered and wide/tall enough.