CAN Bus Emulation using Digital

In quite a few environments it is frowned upon to have active components in Operational Test Program Set Hardware (OTPH). This is usually due to obsolescence and complexity concerns of the Interface Test Adapter (ITA). The controlling organization normally desires that ITA's be as passive as possible. There are many reasons for this such as the afore mentioned obsolescence, complexity of the ITA, and the requirement for the ITA to remain in service for 20 years or more. The Controller Area Network (CAN) bus is very popular in the automotive industry. However, it is also used in military applications due to its simplicity, noise immunity and low cost. This brings about an issue because implementing a CAN bus normally entails using one of the commercially available CAN bus controller chips and associated components. Since the number of Test Program Sets (TPSs) using the CAN bus are fairly limited it is unlikely that there will be CAN bus capability available in the Automatic Test Equipment (ATE) that is used to test the Unit Under Test (UUT). Therefore, normally this would require active components in the ITA. Implementing a CAN bus usually requires active components due to the relatively complex way the bus does arbitration and data transfer. The bus uses dominant and recessive bits in a differential bus to transmit data. In a complex CAN bus implementation with multiple devices, it would likely be almost impossible to emulate the CAN bus due to the way the bus architecture handles determining the priority of messages. The emulation device would have to monitor the bus and make decisions in real time. This can be accomplished with an FPGA, but then there are the issues with the dominant and recessive bits which would likely prevent proper emulation. However, if there is only one node attached to the bus the scenario becomes much simpler. This paper will cover one attempt to emulate a CAN bus with instruments already available in the Automatic Test Equipment.