Serial Ports

Ports which communicate the information in a serial basis; i.e. one bit at a time. Examples include:

One-bit-at-a-time (transmits either "0 bit" or "1 bit" signal at any instant):

RS-232 (probably the most ubiquitous of all serial ports)
RS-485
UniversalSerialBus (USB)
I2C (also IIC, InterIntegratedCircuit) Bus
SerialAta? (new replacement for parallel IDE)
Ethernet
PS2
300 bit/s and slower dial-up modems
10Base-T Ethernet (Manchester modulation)
FireWire
Many types of signaling on FiberOptic? cables are serial
<add examples here>

Only one or 2 wires (definitely not parallel, but not one-bit-at-a-time either):

100Base-T Ethernet: 3-level modulation (100BASE-T4 uses 8B/6T) (100BASE-TX and 100BASE-FX use ... something else ?)
1000Base-T Ethernet (GigaBitEthernet?): 5-level modulation on each pair of wires
1200 bit/s and faster dial-up modems: up to 255-level modulation (limited by the telephone network)

Constellation diagrams show all the possible symbols that may be transmitted at any instant, using phase-amplitude modulation. The first group has exactly 2 symbols in their constellation diagram ("2-level modulation"), so they transmit one bit at a time. The second group has more than 2 symbols, so at any instant, they are transmitting one "symbol" that conveys more than one bit of information.

Doesn't 100 Base-T Ethernet also combine bits in a more complex manner? (using phase and amplitude changes, just as are used by modern modems)

Yes, but not quite as complicated.

CategoryHardware