In SX Microcontrollers, SX/B Compiler and SX-Key Tool, phipi wrote:

Peter,

That should work. But I'd be more inclined to run it through a transistor driver. The reason is that, by relying on the pin tri-stating, your source impedance is constantly changing. This could have an impact with long cable runs. With a transistor driver, you can get a 75-ohm source impedance, without having to fiddle with the resistor divider values. Higher-valued divider resistors also put less stress on the microcontroller pins, and the transistor isolates it somewhat from transmission line issues.

Attached is a sample schematic. It's an emitter follower whose source impedance is determined largely by the collector resistor. This circuit will output a 1V p-p signal regardless of whether the monitor it's feeding is properly terminated. Due to the interposed B-E junction, the sync tips will be at 0.6V instead of 1.2V.

-Phil

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