The SPI bus in the automotive sector


What is SPI?

The Serial Peripheral Interface (SPI) is a serial bus that was developed for master-slave operation between microprocessors and Motorola components. The synchronously working SPI bus is comparable to the I2C bus from Philips and Microwire from National Semiconductor, but it is faster than the I2C bus and is particularly suitable for applications with irregular access, for example for communication between microprocessors and chips for the signal processing.





Where is SPI used?

SPI is mainly used within the device for communication between different circuit parts, e.g. B. between a controller and peripheral ICs. An example of this is a temperature sensor, microcontroller and EEPROM. The microcontroller reads out the sensor and saves the data on the EEPROM. The complete data exchange takes place via SPI. The advantage of SPI with regard to the alternative I2C is the much higher data speed.







What is the problem of SPI in the automotive sector?

Because there are only two wires, the addressing and confirmation overhead is very complex to handle. The SPI bus is unsuitable for meter-long transmissions, especially in the automotive sector, where there are also many interfering influences in the signal transmission, such as the ignition or the alternator. More suitable communication protocols such as CAN or RS-485 are preferred for vehicle internal networks.



SPI ICs for the automotive sector

Since the SPI components such as EEPROMs are subject to more difficult environmental influences and have to meet high requirements, various IC manufacturers offer components specially manufactured for this purpose that have a higher temperature tolerance and are less prone to failure.





AT24C04B EEPROM MicrochipAutomotive IC example

An example of a SPI IC specially manufactured for the automotive sector are the AT25080B, AT25160B, AT25320B, and AT25640B from Microchip (ATMEL), whose temperature operating range (class 1) has been extended and are particularly energy-efficient. Temperature range class 1: -40 ° C to 125 ° C.



Tools for SPI



In order to test I2C modules, a corresponding master is required which queries the slave ICs and controls them if necessary. The Aardvark I2C Host Adapter is an interface that allows developers to access the SPI bus directly from their PC. The Aardvark I2C / SPI Host Adapter is connected via USB and can transfer the serial data streams using the I2C and SPI protocols. With the Aardvark SPI system configurations can be simulated, developed and tested. In addition, it has a comprehensive programming IC library with which the relevant IC can be programmed with one click from the developer's PC.






An oscilloscope is not sufficient to identify bus or transmission errors in long transmissions and to discover their origin due to the insufficient memory depth. A protocol analyzer is recommended for debugging SPI. The Beagle I2C / SPI analyzer is a high-performance monitoring solution in a compact, portable device.