It seems either TTL(74HCT2G32) or CMOS(74HC2G32) now all use MOSFET internally in input side of OR gate. The sink current in input side should only takes under 1uA. So it shouldn't cause any issue when parallel it with actual circuit in normal RS232 application (communication speed less than 500Khz). Or am I wrong?
Correct except that 74HCTxxx series are not TTL. HCT is short for High-speed CMOS with TTL compatible I/O meaning they have low VIH
and high IOH
satisfying TTL compatibility. What I was referring to as TTL was something like this:http://eecs.evansville.edu/home/resources/pdf/dm7432.pdf
Two diodes and a resistor before the led instead of OR gate is enough.
Practical but might still cause trouble in case of parallel connected receiver if not buffered.