Serial Communications

What actually is Serial communication?

To put it simply, Serial communication refers to the process of sending data one bit at a time, sequentially. This is performed over either a "communication channel" or a "computer bus." The contrast to serial communication is "Parallel Communication," in which several bits are sent as a whole over a link with multiple parallel channels.

Why do we use serial over parallel communications?

Data Transmission

Think of each system as a road. In a parallel cable (8-bit, 16-bit, 32-bit, 64-bit, 128-bit), you have one lane per bit. When all of those lanes hit the junction (receiver), they must stop and stabilize before they can move on, leading to congestion. In a serial system, there is only one or sometimes two lanes (full-duplex connection). Due to the nature of Serial Communications the data is never held up like traffic at a junction, as only one bit of data can be in any lane at a time.

Simplification

Serial connections also require fewer wires, 3 for Half Duplex or 5 for Full Duplex, whereas parallel connections require one wire per bit. So, an 8-bit parallel line requires 9 wires.

Crosstalk

Parallel connections are naturally more prone to crosstalk. Signals traveling on one wire can interfere with signals on another nearby wire, leading to data errors.

Distance

Serial connections are better suited for long-distance transmissions due to their almost perfect data accuracy at high speeds.

Benefits of parallel over serial communication

The key benefit of parallel communication is speed. As a general rule, more wires = more speed. In the correct applications, with careful engineering to iron out bit-level timing issues, the data transfer potential of parallel communications can far exceed that of serial communications.

Full or Half Duplex?

What do we mean by duplex?

A duplex communication system refers to any point-to-point (PTP) system composed of two or more connected devices that can communicate with each other in both directions. There are two common duplex communication systems: Full-Duplex (FDX) and Half-Duplex (HDX).

What’s the difference?

In a Full-Duplex system, communication can occur in both directions simultaneously. Old-style telephone service lines are a prime example of an FDX communication system—both parties can speak and be heard by the other party at the same time, with a constant channel each way between them.

In a Half-Duplex (also known as semi-duplex) system, communication can only occur one way at a time. If device A wants to send data to device B, but device B is already sending data to device A, then device A must wait until device B has finished transmitting before sending its data.

Most Common Serial Architectures

The most common Serial Architectures are listed below:

• USB -> Universal Serial Bus
• SPI -> Serial Peripheral Interface
• I²C -> I²C (Inter-Integrated Circuit)
• CAN -> Controller Area Network
• Modbus -> MODBUS
• UART -> Universal Asynchronous Receiver-Transmitter
• HDMI -> High-Definition Multimedia Interface (Note: HDMI is not a typical serial communication protocol like SPI or I²C but uses serial transmission.)

Most Common Serial Architectures in the Fire & Security Industry

The most common Serial Architectures found within the fire & security industry are listed below:

• RS-485
• RS-232
• RS-423
• RS-422