What is ISO 20794‑4 about?
ISO 20794‑4 is part four of the multi-series standard that specifies the CXPI data link layer and the CXPI physical layer.
The DLL is based on:
- Priority-based CXPI network access
- Non-destructive content-based arbitration
- Broadcast frame transfer and acceptance filtering
- Node related error detection and error signalling
The CXPI physical layer (PHY) requirements comprise of:
- Physical signalling (PS) sub-layer, which specifies the requirements of the clock generation function, the encoding and decoding of CXPI frames, and bit-wise collision resolution logic
- Physical media attachment (PMA) sub-layer, which specifies the requirements of the signal shaping waveform logic
- Physical media dependent (PMD) sub-layer, which specifies the requirements of the CXPI network termination, electrostatic discharge protection, etc., and device connector requirements
- Physical media (PM), which specifies the requirements of the CXPI network cable/wiring harness
Who is ISO 20794‑4 for?
ISO 20794‑4 on data link layer and physical layer is useful for:
- Road vehicle manufacturers
- Designers and developers of clock extension peripheral interface (CXPI)
- Automotive engineers
- Vehicle switches and sensors manufacturers
- Data link layer and physical layer designers and developers
Why should you use ISO 20794‑4?
CXPI is an automotive low-speed single-wire network. It is an enabler for reducing vehicle weight and fuel consumption by reducing wire counts to simple devices like switches and sensors.
CXPI serves as and is designed for automotive control applications, for example, door control group, light switch, and HVAC (Heating Ventilation and Air Conditioning) systems.
ISO 20794‑4 describes the data link layer and physical layer for clock extension peripheral interface (CXPI). The data link layer and physical layer:
- Provides long and short data frames
- Adds a frame identifier into the frame
- Adds frame information into the frame
- Adds a cyclic redundancy check into the frame
- Performs byte-wise arbitration and reports the arbitration result to higher osi layers
- Performs frame type detection in reception function
- Performs error detection and reports the result to higher osi layers
- Performs carrier sense multiple access (csma)
- Performs Collision Resolution (CR)
