Waveform for one byte sent over 3.3 V TTL
"You will be using an oscilloscope to investigate the serial port of a Raspberry Pi. One standard for serial communications is RS-232, but the port we will use is 3.3V TTL. Draw the waveform you would expect for one byte sent over this serial link."


So this question is a multi-faceted gem, designed to make students dig into the details of RS-232, TTL, and protocols.  Since it is a coursework question, this "answer" will be Socratic in nature.


What is RS-232? That is an old standard for the electrical parameters for serial communication. Typically this is the wiring, voltages, and "DB" or "D-Sub" connectors used such as DB-9 or DB-25. RS-232 is a specification and states that signalling happens with certain voltage ranges above and beyond 0 volts, such as +/-12v. It is an old standard, so uses larger voltages than we typically use today. It has stuck around however, because it is very robust and long cable lengths are possible. 
What is TTL? TTL means "transistor-transistor logic" and implies digital signals sent between digital chips. So this voltage range is 0-5v for logic low and high. This standard was, for a long time, exclusively 5 volts. Until CMOS came around, with it's capability to do 15v or even 20v. However, with more modern digital chips, this has reduced greatly to 3.3v, 2.5v, or even 1.8v in an effort to save power and increase speed.


Ok so one major difference is that an RS-232 signal will range from +12v to -12v, whereas a TTL signal will range from 0v to +3.3v.

And of course a byte of data is eight bits.

Then you must consider what digital information is being sent; or in other words, the protocol. And at what speed, or baud rate. In a single-wire configuration, provision must be made to indicate when a transmission is starting, so that the receiver knows to "listen." This is called a start-bit. And there may need to be one or more stop bits, with the bits of the actual data in the middle.

So your waveform would look like (0-3.3v):
* Start bit
* Eight bits of data
* Stop bit(s)

Additional research terms: RS-232, TTL, Serial, Protocol, baud rate, start/stop bit, parity.