The state-of-the-art communication protocol for automotive sensors is still the analog output. This is a classic point-to-point connectiona sensor is connected with an ECU and transmits its output signal in form of a voltage level. Despite some improvements that have been made, such as increasing the resolution or the introduction of diagnostic ranges (LDR, UDR, see below), the analog output constitutes the state-of-the-art from the early '90s.
Therefore, the analog output merely allows the transmission of the sensor signal in the signal range (e.g. 10 to 90%) and the failure state through switching the output in the diagnostic ranges: Lower Diagnostic Range (LDR) or Upper Diagnostic Range (UDR). Consequently, more specific and more detailed failure information can not be communicated.
The solution to this problem is digital communication between sensor module and ECU, allowing the transmission of status information, time stamps, and error codes in addition to the sensor data. Unfortunately, the problems created by a change to digital communication are highly complex because of the non-homogenous and highly diversified sensor system component supplier structure (noted below).
On the analog side, a great variety of sensor modules with analog output for all environmental variables are available on the market. Nearly all ECU microcontrollers have analog inputs. Thus it is possible to develop new applications using components that are on the market or require minor design adjustments without problems or major risk.
Such a situation does not apply with a digital communication protocol. Available standard protocols must be employed in a dedicated manner. The digital protocols available include: CAN: Is generally too complex and too expensive for sensors
LIN: Merely allows a low transmission rate of 19,200 baud max
Peripheral Sensor Interface (PAS4, PSI5): Was developed for safety-related applications (e.g. airbag), requires 9V-operating voltage and has a high current consumption
SENT: Only uni-directionally defined; currently in standardization
Thus, proprietary solutions are most commonly used for applications requiring digital communication. This means each circuit manufacturer defines its own protocol. With the ZACWire (serial digital interface) protocol, which supports the ZMD31150, ZMD offers an open standard that provides communication security, and is flexible in terms of baud rate and end-of-line calibration.
The challenge for the coming years is the specification and implementation of a standardized digital interface which takes into account the requirements of sensor systems and applications, and is cost-effective. Three somewhat contrary design conditions must be met through this interface:Circuit test: Maximum communication speed to minimize test costs
Calibration: As simple and flexible as possible
Application: As fast, secure, and compatible as possible, specifically under conditions of out-of-specification operating voltage, high EMC strength, and limits on maximum RF radiation