The voltage ranges for a logic high and a logic low in RS-$232$ C standard is
- Low is $0.0 V$ to $1.8 V$, High is $2.0 V$ to $5.0 V$
- Low is $-15.0 V$ to $-3.0 V$, High is $3.0 V$ to $15.0 V$
- Low is $3.0 V$ to $15.0 V$, High is $-3.0 V$ to $-15.0 V$
- Low is $2.0 V$ to $5.0 V$, High is $0.0 V$ to $1.8 V$