Effects of Capacitive Bus Loading on J1850 Vehicle Networks

Capacitive overloading of SAE J1850 vehicle communications networks will cause a change in the time constant for a particular network causing it to fall out of specification. Addition of transient voltage protection devices to communications nodes increases a node's capacitive load on a system causing the overall network time constant to change. Other capacitive components commonly encountered in a communications network will also change the network's time constant, causing it to fail or to behave erratically. Component selection plays an important role in maintaining the correct capacitive loading on a SAE J1850 network in order to adhere to the physical layer characteristics of both PWM and VPW protocols.