In Electronics parlance, you may say:
"signal A latches signal B when input L is active"
signal A gathers and stores the value of signal B when input L is active
It is similar to taking a snapshot were the scenery is the values of electronic signals.
'Latched on to signal B' seems to me to mean:
the latching function is active, and is registering the value of signal B
I have to latch on to calculus in order to understand the Physics lessons.
Meaning: I have to start to understand the subject of calculus in order to ...