The CMU200 can output its screen to an external VGA monitor – fairly standard 640 x 480 pixels mode – and senses at boot whether such a monitor is connected; otherwise, this output remains disabled.
I have several CMUs and want to use a ‘mechanical’ VGA switch to select which CMUs screen to show on a monitor (and at the same time send it to a video-grabbing device). Because of the sensing part, my current procedure is rather cumbersome: I need to select each CMU one by one on the VGA switch, have it boot up, then go to the next one, etc. I would rather be able to turn all CMUs and make them all believe there is a monitor connected.
Doing some quick search, I understand that, over time, different methods were used to sense a monitor via VGA:
- A resistance of 75 ohms between each video output line (R, G, B) to ground.
- Connect any (combination) of the Monitor ID Bits (pin 11, 12, and 15 for bit0, bit1 and bit2, respectively).
- An I2C signal (SDA on pin 12, SLC on pin 15), used by the VGA Video BIOS to access a 128 byte or 256 byte serial EEPROM memory in the monitor to determine its specifications.
Before I go into measuring and digging this out, is there anyone that knows how the CMU senses the presence of a monitor? If yes, that would be quite helpful…
I have a bit of the same question for my AMU200A. It has a more advanced video card than the CMU, and runs Windows XP Embedded, and may or may not sense the monitor the same way as the CMU does…
Thanks! Rudi