>>2929363
Probably not on newer MCUs. An older type like the ATmega328 (arudino uno mcu) would be able to but newer types would likely see a significant rise in Vol when trying to sink 15mA. You might see 1v when you should be seeing under 100mV. The exact voltage rise would be dependent on the mcu and may or may not be acceptable depending on the characteristics of you optoisolator. Also, I would be careful putting 5v on a digital input if the mcu is unknown. Newer types would may run on 3.3v rather than 5v and there is no guarantee that the pins would be 5v tolerant. Since 19200bps is very slow by modern standards, I would buffer the output with a transistor. I imagine the LED on the optoisolator is connected to 5v through a resistor and you want to connect the cathode to the mcu pin to turn it on when the pin is low? If that is the case you can go with normal non-inverted logic and connect the tx pin on the mcu to a bjt inverter. pic related