640x480 on LC II?

[johnklos]

After seeing mention about how the LC and LC II can do monochrome video when no VRAM is installed, I tried it. It didn't work. Then again, my multiscan adapter only works with my LC II in 512x384 mode. So, even though the machine booted, nothing beyond the boot grey appeared on the screen (the boot grey is unlike other models - it comes on immediately on power up).

After checking in Apple Service Technical Procedures, I see that it is only supposed to work in 640x480 mode (Basics, 1.18):

[SIZE=12pt]When [/SIZE][SIZE=11pt]using a video [/SIZE][SIZE=10pt]SIMM [/SIZE][SIZE=12pt]without [/SIZE][SIZE=10pt]VRAM, [/SIZE][SIZE=12pt]the [/SIZE][SIZE=11pt]built-in video chip [/SIZE][SIZE=12pt]supports [/SIZE][SIZE=10pt]640 [/SIZE][SIZE=11pt]x [/SIZE][SIZE=10pt]480 [/SIZE][SIZE=12pt]screens [/SIZE][SIZE=11pt]only, [/SIZE][SIZE=12pt]at [/SIZE][SIZE=10pt]1[/SIZE][SIZE=11pt]bit/pixel.[/SIZE]

Does anyone know what I'd have to do to make the LC II run at 640x480? Do I need a diode across pins 7 and 10 of the video connector, like in the first diagram here?

 

[Cory5412]

I believe the LC II only supports fixed-sync displays * )or some of Apple's own multiple scan displays that could specify what monitor they were), so you'll have to either use one of those configurable fixed-sync adapters, or a Mac-specific fixed sync display, such as one of Apple's own monitors.

I have an LC and I had an LC II long ago and both did 640x480 with the adapter I had (one of the configurable ones with DIP switches) and on Apple's own displays, such as the AudioVision and the High Resolution RGB display.

 

[Gorgonops]

Those old "dial-a-res" adapters are really useful for cases like this.

I believe the LC II only supports fixed-sync displays

I may be mis-remembering this, but I vaguely recall that one of the selling points of the LC was that it could support 640x480@60hz in addition to the Apple standard 67hz when paired with the right adapter, which made it possible to use (by this point far cheaper) generic VGA monitors?

That said, if that weird no-vram monochrome mode actually exists something tells me it's hardwired to run at the Apple standard refresh rate.

 

[Cory5412]

Just looking at the LEM profile for the LC II, if I had to guess what was happening (and, this is a guess because I haven't looked for the dev note or service manual for this machine) it's using main system RAM and in an effort to avoid using too much of that, given the low ceiling and low amount they shipped with to begin with, that is why it's limited to 1-bit. (this is confirmed on the 20th page of the above linked PDF, which I just opened while writing this post.) The sync frequency probably doesn't matter in that case.

As it stands, it looks like you need to (or "can") upgrade it to 512k to get 8-bit at 640x480 (or 16-bit at 512x384).

Just thinking about it, it seems kind of wild that Apple would even have bothered to design a 1-bit graphics mode that works without any VRAM installed.

The confusing wording is on the 31st page, "When using a video SIMM without VRAM" which to me indicates that you can put something in that VRAM slot that's not VRAM, and if you do that, there's a 1-bit/640x480 limitation on the output. Which, is a different state than running the system with 0kb of installed VRAM and using the top megabyte of memory, which seems like it should allow more color but will likely incur a penalty on overall system performance. (EDIT: I might just be misreading it, especially since it only mentions this limitation the second or third time the possibility of running the system with 0kb of video memory is mentioned.)

I would try this out on my own, but my LC is in storage. Perhaps it's time for me to go to Kingman (where my storage locker is).

 

[Gorgonops]

Just thinking about it, it seems kind of wild that Apple would even have bothered to design a 1-bit graphics mode that works without any VRAM installed.

The one reason that would make sense is if they were planning to use the same chipset in a toaster Mac upgrade. The Classic II is *almost* that Mac, but not quite.

One crazy possibility: could they have been thinking about a 12" screen compact as a counterpart to the education-focused PS/2 Model 25? (which came in a monochrome version)

An LC with a monochrome monitor on top is basically the same thing, though.

 

[Cory5412]

Now I've got a mental image of something between the Classic/II and the LC520 (or, the "Mondo" prototype from AppleDesign, if anybody remembers that one) rattling around in my brain.

Time to put that mental image in Danamania's brain.

 

[jessenator]

I like this prototype. Comes pre-yellowed even  

 

 

[Toni_]

This is an interesting topic, did any of you manage to get the zero-VRAM monochrome mode to work?

I dug out my LC 2 tonight from the storage closet, remove the VRAM, and went through all my VGA adapters to check which of them would work. Most of them did not give any output to VGA, but two of them (which I believe are hardwired to 640x480 sync-on-green) gave output on a VGA monitor - BUT the output was only only full screen of gray color which I guess is the output given by any mac video cards before it is initialized (not the black&white pattern, but solid 50% gray).

However, after I connected a real 14" Macintosh Color Display, I got rather odd pattern on the screen:



Unlike the 50% gray on VGA adapters in previous attempts, there appears to be 16 pixels of some data on the screen which gets repeated for the whole screen (40 times horizontally x 16 = 640 pixels). It does not appear however to be actual, real video data, as the 16 bit data seems to change randomly when anything happens during the boot.

Everything works normally though, when booted with the 512K VRAM installed (in picture laying on top of LC II case).

 

[Gorgonops]

This is probably a dumb question I could likely answer by looking up the documentation for the Apple video port sense lines, but... does the Apple sense line arrangement allow a Mac to tell the difference between a monochrome and color monitor? VGA originally used a specific pin(*) for that; when said pin was grounded that would signal the VGA BIOS to basically lock the three DACs together and use a default palette that mapped colors to shades of gray. Perhaps this special one-bit mode is only available if the Mac *specifically* believes it has a mono monitor attached?

(* Geek note: this pin was reused for the DDC display channel, so technically monochrome VGA monitors are *slightly* incompatible with VGA cards that support DDC.)

 

[Gorgonops]

... From an old TIL article, this is supposedly the pinout of the 12" Mono "high-res" monitor:

Apple mono 12" monitor:
1 - unused
2 - unused
3 - comp H and V sync
4 - mon ID bit 1 grounded
5 - mono video
6 - mono grn
7 - mon ID bit 2 open
8 - unused
9 - unused
10- mon ID bit 3 open
11- csync ground
12- unused
13- unused
14- unused
15- unused

Source:

http://www.retrotechnology.com/herbs_stuff/macmons.txt

However, this source says that the Hi-Res mono and 13" Hi-Res color haev the same sense line arrangement. So...?

http://old.pinouts.ru/VideoCables/MacVideoToVGA_pinout.shtml

Does the 14" color monitor register the same way as a 13" fixed-frequency, or is it multi-mode capable?

 

[Toni_]

This is probably a dumb question I could likely answer by looking up the documentation for the Apple video port sense lines, but... does the Apple sense line arrangement allow a Mac to tell the difference between a monochrome and color monitor? VGA originally used a specific pin(*) for that; when said pin was grounded that would signal the VGA BIOS to basically lock the three DACs together and use a default palette that mapped colors to shades of gray. Perhaps this special one-bit mode is only available if the Mac *specifically* believes it has a mono monitor attached?

(* Geek note: this pin was reused for the DDC display channel, so technically monochrome VGA monitors are *slightly* incompatible with VGA cards that support DDC.)

That's a good point, I luckily had a Macintosh 12" Monochrome Monitor also stashed away so tried with it now too:



Sadly, it appears to have same output. However, I did notice there was vague "ghost" image of "Welcome to Macintosh" screen visible during the boot, so I'm guessing my LC II may have some kind of hardware failure that's specifically appearing when using the built-in monochrome mode...

 

[johnklos]

Welp. I tried on my LC II, too. I even found a monitor adapter with switches, set the screen depth to 1 bit, and removed the VRAM. I get the grey screen and that's all. The machine boots, but I can't see anything.

While looking for the monitor adapter with switches, I came across a 512K VRAM SIMM, so I guess I don't need to do this anyway, but I was definitely curious