Question

In a CAN bus, there are three computers: Computer A, Computer B, and Computer C. The messages being sent are 1.5 milliseconds long. Computer A starts sending a message on the bus; 500 microseconds later, Computer B starts to send a message, and 250 microseconds after that, Computer C starts to send a message. When does Computer A retransmit its message?

A)	After 1 millisecond

B)	After 2.25 milliseconds

C)	Never; Computer A will not retransmit.

D)	After 2 milliseconds

Answer 1

b). After 2.25 milliseconds

A Controller Area Network (CAN bus) is a robust vehicle bus standard designed to allow microcontrollers and devices to communicate with each other in applications without a host computer. It is a message-based protocol, designed originally for multiplex electrical wiring within automobiles to save on copper, but is also used in many other contexts.

Therefore, the computer A can retransmit in 1.5+0.5+0.25=2.25ms. for to not be in signal contention and with no losses.

CAN data transmission uses a lossless bitwise arbitration method of contention resolution. This arbitration method requires all nodes on the CAN network to be synchronized to sample every bit on the CAN network at the same time. This is why some call CAN synchronous.