I have the circuit structure that looks as shown below. An I/O signal, sigA, (active low) is driving the P1 port on unit U1. An NMOS transistor's drain is connected to this signal with the gate/source/bulk connected to ground. How does this NMOS transistor work and what is its purpose?
The gate/source are connected to ground, so I am not sure how current will flow through (i.e., what condition will make M1 turn on). It looks like a pull down device, but since sigA is active low, it doesn't make sense to me.