Question

(TCO 4) In a CAN bus, there are three computers: Computer A, Computer B, and Computer C. The messages being sent are 2 milliseconds long. Computer A starts sending a message on the bus; 250 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 2.5 milliseconds
B) After 1 millisecond
C) After 1.5 milliseconds
D) Never; Computer A will not retransmit.

Answer 1

Answer:

A) After 2.5 milliseconds

Explanation:

Given that :

In a CAN bus, there are three computers: Computer A, Computer B, and Computer C.

Length in time of the message sent are 2 milliseconds long

As the computer start sending the message; the message are being sent at a message duration rate of 2 milliseconds

250 microseconds later, Computer B starts to send a message; There is a delay of 250 microseconds = 0.25 milliseconds here at Computer B

and 250 microseconds after that, Computer C starts to send a message

Similarly; delay at Computer C = 0.25 milliseconds

Assuming $T_{RT}$ is the retransmit time for Computer A to retransmit its message, Then :

$T_{RT}$ = $T_A + T_B + T_C$

$T_{RT}$ = 2 milliseconds + 0.25 milliseconds + 0.25 milliseconds

$T_{RT}$ = 2.5 milliseconds

Thus; the correct option is A) After 2.5 milliseconds