Apple MiniDisplayPort to VGA adapter disassembly

[edwardgeo]

Disassembly of Apple dongle and pinout. Photos attached soon

 

[joevt]

The ADV7123 JSTZ240 is the triple 10 bit DAC - I guess 240 = 240MHz.
https://www.analog.com/en/products/adv7123.html
But I don't think Apple allows more than 160MHz for VGA adapters? I had to make a patch for Intel Graphics to get 330 MHz (for DisplayPort to VGA adapters)
Anyway, 160MHz is enough for the 1920x1200 60Hz advertised limit but only if you're using CVT-RB. For CRT displays, CVT or GTF is the usual timing calculation, in which case almost 200MHz is required.

The gm58007 is a mystery. Maybe it's a DisplayPort to HDMI 1.1 adapter? I think it's easier to get the 10 bits each for red/green/blue with an HDMI signal.
https://debugmo.de/2009/05/and-you-thought-a-keyboard-firmware-upgrade-would-be-far-fetched/
Or more likely it's a microcontroller with some DisplayPort handling capability.
Or maybe the adapter uses DisplayPort Dual Mode (DP++) so the input to the microcontroller is actually HDMI using DisplayPort voltages.
Did you check the adapter to see if it reports DisplayPort DPCD registers (in AGDCDiagnose output from macOS or i915 in Linux)?
If it's DP++ instead of DP then it might not be restricted to 160MHz?

Actually, I have this adapter (A1703). Trying it now. It has two lanes of DisplayPort 1.1 HBR link rate so the limit of 10bpc should be 144MHz and the limit at 8bpc should be 180MHz.
It has Apple firmware (OUI matches Apple). The default mode is 8bpc so maybe it doesn't support 10bpc. One of the modes it can do on my CRT is 1400x1050 85Hz 179.5MHz 8bpc (using Monterey, Mac mini 2018, W5700) but the image is wavy on my CRT (it's old). Lower refresh rate (60Hz) is not wavy so maybe the problem is the GPU/adapter. I guess the 160MHz limit doesn't apply to AMD. The firmware reported in AGDCDiagnose is HW Version 1, FW Version 1.3. I don't know if that's the latest firmware.

If it's only two lanes, then at least 4 of the DisplayPort pins are unused.