Can bus doubts and answers

1 can bus 2 data cable is how to represent data information 1 and 0?

The can bus uses the differential data representation method, usually 2 data line is 2.5V, indicates the recessive (1). When using data 0 (dominant) need to send 1 with the data line up to 3.5V another down to 1.5V. A is shown

All nodes are connected to these two data lines, and when all the nodes are sending data as recessive, the bus data is represented as recessive, and if one of the nodes sends the data dominant the bus data is represented as dominant. Data arbitration is also based on such a feature of arbitration.

2 Can bus there is no clock between the nodes, if the clock frequency is inconsistent between the nodes or even if the clock frequency is exactly the same but the phase offset, how does it realize the synchronization of each node?

The standard bit rate of the network, which is the position time (also known as the standard bit period). As shown in 1, the can bus's rated time is composed of 4 parts: The synchronization segment (SYNC_SEG), the transmission segment (PROP_SEG), the phase buffer Segment 1 (PSEG1) and the phase Buffer Segment 2 (PSEG2). So the rated bit time, the bit period of these segments can be programmed, and can be used in the whole number of basic time units ( time share TQ) to represent. This basic time unit is divided by the oscillator, (BRP is the baud rate prescaler factor, can also be programmed).

Figure 1 The structure of the CAN bus position time

2.1 Hard Sync

Hard synchronization is done only when the bus is idle through a falling edge (the start of the frame), where the bit time of all nodes restarts regardless of the phase error. Forcing a transition along a hard synchronization to a synchronized segment (SS) that is located at the restarted bit time

2.2 Re-sync

In the subsequent bits of the message frame, whenever there is a transition from "recessive bit" to "dominant bit", and the jump falls outside the synchronization segment, a resynchronization is caused. The resynchronization mechanism can increase or shorten the bit time according to the hopping edge to adjust the location of the sampling point , ensure the correct sampling

3 What is the frame type of can bus and the role of various frame types? 3.1 Data Frame 3.2 Remote Frame 3.3 Error Frame 3.4 overload frame 4 can bus send data and reply ack

Each type of frame data will have 2 bit stealth data (00) for the ACK, when the first received data node will be the last 1 bit of stealth data to the explicit data (01), the sender if the detection of ACK to become dominant indicates that at least one node received data.

5 can bus how to indicate the bus is idle state?

If there are 11 consecutive hidden data in the bus, the bus is idle.

Can bus doubts and answers