CAN Notes (12) synchronized

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1. synchronization mismatch

CAN protocol is a communication method of the NRZ (Non-the Return to Zero) mode
at the beginning or end of the respective bits have no additional synchronization signal
transmitting unit in synchronization with the timing of the start bit to transmit data

Further, the receiving unit synchronizes the change on the bus level and reception operation

However, the transmitting unit and the receiving unit clock frequency error and (cables, drive, etc.) on a transmission path phase delay can cause synchronization error
thus received by means of hardware synchronization or resynchronization method for adjusting the timing of receiving

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2. Hardware Synchronization

The receiving unit in the bus idle state is detected when a frame synchronization adjustment start
where an edge is detected irrespective of the value of the resynchronization SJW compensation, and that the synchronous segment SS

Hardware synchronization process:

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3. resynchronization

In the receiving process synchronization adjustment for a level change is detected on the bus,
each time an edge is detected, according to the value of SJW by lengthening section PBS1, PBS2 or shortened period to adjust synchronization

However, if the error value exceeds SJW occurs, the adjustment amount can not exceed the maximum value SJW

Resynchronization:

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4. Adjust the synchronization rules

Hardware synchronization and resynchronization comply with the following rules:

1. A bit synchronization adjustment only once
2. Only the bus when the bus value from the previous sample point and not the same edge, which edge can be used to adjust synchronization
3. The bus is idle and the presence of a recessive to dominant signal edge , then must be synchronized hardware
4. The bus is not idle recessive level detected when the edge of the dominant level if the condition 1 and 2, will be re-synchronization
   , but also to meet the following conditions:
   4.1 to the observed transmission unit itself dominant level output when there is not re-synchronization delay
   the case of 4.2. in the start of frame transmission to the arbitration unit section has a plurality of cells simultaneously transmitted, without delay edge resynchronization

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Reference:
"CAN Primer"

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Related Recommended:
CAN Notes (11) Bit Timing
CAN Notes (10) and an output error type
CAN notes (9) bit stuffing
CAN Notes (8) priority
CAN Notes (. 7) CAN protocol (II)

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