Mac Display information

[sfiera]

I spent a while today getting my head around sense pins and timing for old Macintosh (DA-15) displays. Here is the writeup:

Mac Tech: Displays

This is a result of online information-gathering, a little hypothesizing, as well as probing my UnimacFly VGA adapter with a multimeter. Its dip switches appear to correspond to pins [11, 4, 7, 10, X, 10→7, 7→10, X], and knowing that, there are additional output modes you can try, like 512×384 (11011001) and 640×870 (10101001).

There’s more information I’d like to include, such as a schematic for building your own adapter.

 

[sfiera]

Oh, I assumed the 640×400 option was for Apple II emulation, but it’s the IIgs’s resolution, so that explanation doesn’t really make sense. And:

The Macintosh LC III supports a 640 x 400 video mode that allows users to display 16-bit color on 13-inch RGB and VGA monitors without having to purchase additional VRAM. Users can select this mode from the Options menu in the Monitors control panel.

So I take it that this is implicitly supported on 680×480 monitors.

 

[sfiera]

Does anyone have an Apple Multiple Scan 14 Display and a multimeter? One of the things I’m wondering about is the sense code for a multi-scan display that accepts up to 800×600.

In my VGA adapter, this is indicated by wiring diodes both ways between pins 7 and 10. In theory, the computer could detect that the diodes are present from the voltage drop, but that seems unnecessarily complicated. I would guess that it drives each pin low and checks if the other one goes low, without caring about diodes or voltage drop. The diode arrangement just happens to be convenient in the VGA adapter, since there are already dip switches assigned to the diodes for 1024×768 and 1152×870.

Is someone able to measure the voltage drop across these pins? I’m guessing that there isn’t any, and the pins are wired directly together.

 

[sfiera]

Ah, found it in Technote HW30: http://mirror.informatimago.com/next/developer.apple.com/technotes/hw/pdf/hw_30.pdf

Confirms that the diodes aren’t necessary. For the Multiple Scan 14”, just wire Sense1 and Sense2 together.

 

[Dandu]

One thing to know : i have a 12" monochome and the display works only with old Macintosh.

I have searched many times to found a solution : the display need composite sync avec many modern computer don't do that with adapter. I have made an adapter for that : https://www.journaldulapin.com/2020/01/06/ecran-monochrome/