Serial Protocols
Digital systems are based on the concept of bits, in addition to using bits they often have to transfer them back and forth usually between two components (MCU and Sensor, LCD etc).
🟠 All the different methods of bit transfer can be divided into 2 categories - Parallel and Serial transfer
Serial Protocol fundamentals
Parallel transfer
The earliest protocols for transmitting data were mostly parallel.
In parallel data transmission, many bits are transmitted simultaneously over many separate channels from a transmitter to a receiver.
Good for short distances, have simple time synchronization and are fairly easy to analyze.
Simple to implement, inexpensive, but very difficult to scale due to the many pins needed to transmit and receive information, low speed and distance. Almost never used today.
Serial transfer
Serial transmission transfers one bit at a time over a bus that can be used by multiple nodes simultaneously.
In addition to the data line, there may be synchronization, control, monitoring, etc. lines.
Such transmission can be synchronous and asynchronous.
- synchronous - uses a separate clock signal to determine the moment of reading the signals.
- support over long distances
- higher throughput
- a larger number of potential nodes. Most modern serial data transmission protocols use multiple channels (buses, wires). This type of transmission becomes more complex to create and analyze.
Families of Serial Protocols
| Low-speed (General) | Automotive | Aerospace / Defence | High-speed | MIPI |
|---|---|---|---|---|
|
UART I2C SPI |
CAN – high speed application, often used with sensorsLIN – low speed. Usually works with car accessories – windows, mirrors, etc.FlexRay – for critical parts of the car, such as braking. Reliability, speed and redundancy.
|
MIL-STD-1553, etc | USB, PCIe, etc | RFFE, SPMI, etc |
Levels, Timing, Framing, Protocols
Levels - answers the question of what voltage is used to represent zero and one.
Timing - determines how often bits should be sent and read.
Framing - determines how the bits will be organized into groups, in what order (idle, start, data, arc, stop..) and what the transitions between groups mean.
Protocols - a set of rules for exchanging information, in additional to the previous characteristics.
Serial Protocols Decoding
A modern approach to analyzing and decoding serial data transmission protocols is the use of an oscilloscope.
After selecting a suitable protocol, it is necessary to set the synchronization and framing levels on the oscilloscope in accordance with the signal that needs to be analyzed, and then connect.
Oscilloscope - is the most common pin-tool for decoding and analyzing parallel and serial protocols.
analog method- when each data transmission line is connected to a separate analog optical channel of the oscilloscope through probes, and the software built into the oscilloscope shows some graphs for analysis.digital or logical- connecting a sensor that interprets the input data as digital signals. A larger number of lines \ wires are available.