The serial peripheral interface (SPI) bus is an unbalanced or single-ended serial interface designed for short-distance communication between integrated circuits. Typically, a master device exchanges data with one or multiple slave devices. The data exchange is full-duplex and requires synchronization to an interface clock signal. However, recent trends in the design of industrial data-acquisition systems have not taken this synchronization requirement into account, and distances between the microcontroller and the corresponding analog-to-digital and digital-to-analog converters (ADCs and DACs) can reach 100 m or more.
The impact of the added propagation delay on the data-to-clock synchronicity is often ignored, and interface designs that operate perfectly in the lab environment cease operation when implemented on the factory floor. There can be multiple reasons for the interface malfunction. This article tries to shed light on the major ones, including:
- Lack of synchronization due to large propagation delays of the signal path
- Reduced noise immunity due to long-distance, unbalanced signal paths
- Damaged transceivers due to large ground-potential differences (GPDs)
- Data transmission errors due to unterminated data lines
- Transceiver latch-up and network downtime due to large electrical transients