are the pins PRE the same as SET, and the CLR the same as RESET ?

PRE (preset) = SET
CLR (clear) = RESET
ADDED:
D and CLK should be connected to Ground.

 

I'm looking at SN74LVC2G74 or SN74LVC1G74 from TI as a single channel equivalent with CLR and PRE pins . I'll see how this works out.

 

View attachment 226234

I'm struggling to understand the input connections to the pair of opto isolators. I can understand the connection to U1, which will trigger the output when the input is high. How does U2 trigger an output ?

 

I'm struggling to understand the input connections to the pair of opto isolators. I can understand the connection to U1, which will trigger the output when the input is high. How does U2 trigger an output ?

Look at this: