Mechanical and electrical specifications

AIS1200PS

10/21

DocID024648 Rev 4

2.4

Sensor communication interface

The AIS1200PS is a single-axis accelerometer with a PSI5 v.1.3 asynchronous

communication interface (PSI5-A). PSI5-A describes a point-to-point connection for

unidirectional, asynchronous data transmission. The sensor is connected to the ECU by two

wires. After switching on the power supply, the sensor starts transmitting data to the ECU

periodically. Timing and repetition rate of the data transmission are controlled by the sensor.

2.4.1

Physical layer

PSI5 uses two wires for both power supplies to the sensors and data transmission. The

ECU provides a preregulated voltage to the sensor. Data transmission from the sensor to

the ECU is done by current modulation on the power supply lines. Current oscillations are

damped by the ECU.

Bit encoding is done by a “low” level (IS,Low) which is represented by the normal (quiescent)

current consumption of the sensor(s); a “high” level (IS,High) which is generated by an

increased current sink of the sensor (IS,Low + IS). The current modulation is detected within

the receiver ASIC.

Figure 4. Bit encoding using supply current modulation

Manchester coding is used for data transmission. A logic “0” is represented by a rising slope

and a logic “1” by a falling slope of the current in the middle of TBit (125 kbps  8 μs ± 5%).

2.4.2

Data link layer

Each AIS1200 PSI5 data frame consists of 13 bits containing two start bits and one parity bit

with even parity and 10 data bits. Data bits are transmitted LSB first. The data frames are

sent periodically from the sensor to the ECU at intervals Tref of 224 μs (typ).