The correct answer is: TRUE.
A level shifter is a device that converts the voltage levels between two different logic families. RS-232 is a serial communication standard that uses voltage levels of +12 V and -12 V. Transistor-transistor logic (TTL) is a family of digital logic circuits that uses voltage levels of 0 V and 5 V.
A level shifter is necessary when connecting RS-232 devices to TTL devices, because the voltage levels are not compatible. The level shifter will convert the RS-232 voltage levels to TTL voltage levels, and vice versa.
There are two main types of level shifters: passive and active. Passive level shifters use resistors and capacitors to convert the voltage levels. Active level shifters use transistors to convert the voltage levels.
Passive level shifters are simpler and less expensive than active level shifters. However, they are not as efficient and can cause signal degradation. Active level shifters are more efficient and can provide better signal quality.
The type of level shifter that is used depends on the application. For example, if the application requires high signal quality, then an active level shifter should be used. If the application is not as sensitive to signal quality, then a passive level shifter can be used.