This feature allows the operator to monitor five channels of serial communication protocols typically available on ECUs: CAN (two channels), and J1850  / K-Line / Low-Speed CAN (LS-CAN) (one channel of each). The lines monitored are: Primary J1850, K-line, CAN1 High, CAN2 High, LS-CAN.

The signals are routed on the base module card, from the rear ELCO-56 harness connector to the three 9-pin D-Sub connectors mounted on the front panel of the module. They are also made available on female banana-jacks on this same front panel. Refer to the Base module front plate description for pin assignment information.

The inputs are operating voltage tolerant and have an input impedance greater than 100 kΩ. The state of the input is monitored over a one-second window sampled at 1 kHz. 

The figure below shows the monitoring and termination circuit for the CAN channels. The circuit for  LS-CAN, J1850 and K-line are similar, except for specific grounding and termination values (see 4653703 section below).

Sensing unit measurements

The sensing unit measures three values for each signal: the digital current state, the analog current state and the transition count :  

• The analog state is the 8-bit value (0-255) of the voltage value of the line.
• The digital state is the high/low state of the serial line captured at the beginning of the calculation step.
• The transition count is the number of transitions that occurred on the serial line during the previous calculation step. It is limited to 255.

For K-Line, CAN 1- HI, CAN 2-HI and LS CAN input lines, the sensing unit indicates a high when the input voltage is above 3.0 V and a low when the input is below 2.8 V. For the J1850 line, the sensing unit indicates a high when the input voltage is above 4.1 V and a low when the input is below 3.8 V. 

CAN Termination

The board implements a termination resistor circuit for each of the three CAN channels (CAN1, CAN2, and LS-CAN). For CAN1 and CAN2, the termination resistor is 120 Ω, between the High and Low signals. For LS-CAN termination resistor is 2.2 kΩ, between LS-CAN and ground.