The AD723/AD725 is the NTSC encoder microchip we are using for the mbed game console (mbedGC). It requires a clock of 14.31818Mhz, which is 4 times the speed of the NTSC colorburst (3.57Mhz). At the FIU electonics lab, we have access to a frequency generator that we use to generate this timing signal. Something strange happens when you apply 14.0Mhz to the AD723 microchip. A test pattern emerges on screen! Is this intentional? I wouldn’t be surprised. It’s probably a test pattern built into the device to make sure it is working properly.

Other notes: It only happens when you apply 14.000Mhz. It won’t work if you apply 14.1Mhz or 13.9Mhz. This is why we believe it is an intentional test pattern implemented by the designers of the microchip. Thanks Yigal for finding this!