DESIGN OF A CUSTOM ASIC INCORPORATING CAN™ AND 1 ...
DESIGN OF A CUSTOM ASIC INCORPORATING CAN™ AND 1 ... DESIGN OF A CUSTOM ASIC INCORPORATING CAN™ AND 1 ...
3.5.1 Error-Active Figure 3.10 CAN Bus Error States An Error-Active node can actively take part in bus communication, including sending an active-error flag, which consists of six consecutive dominant bits. The Error Flag actively violates the bit stuffing rule and causes all other nodes to send an Error Flag, called the Error Echo Flag, in response. An Active-Error Flag, and the subsequent Error Echo Flag may cause as many as twelve consecutive dominant bits on the bus; six from the Active Error Flag, and zero up to six more from the Error Echo Flag depending upon when each node detects an error on the bus. A node is Error-Active when both the TEC and the REC are below 127. Error-Active is the normal operational mode, allowing the node to transmit and receive without restrictions. 63
3.5.2 Error-Passive A node becomes Error-Passive when either the TEC or REC is equal to or greater than 127. Error-Passive nodes are not permitted to transmit Active-Error Flags on the bus, but instead, transmit Passive-Error Flags which consist of six recessive bits. If the Error-Passive node is currently the only transmitter on the bus, then the passive error flag will violate the bit stuffing rule and the receiving node(s) will respond with Error Flags of their own (either active or passive depending upon their own error state). If the Error-Passive node in question is not the only transmitter (i.e. during arbitration) or is a receiver, then the Passive-Error Flag will have no effect on the bus due to the recessive nature of the error flag. When an Error-Passive node transmits a Passive-Error Flag and detects a dominant bit, it must see the bus as being idle for eight additional bit times after an intermission before recognizing the bus as available. After this time, it will attempt to retransmit. These measures restrict nodes that have a higher than average error rate so that they can’t interfere with communication across the bus. 3.5.3 Bus-Off A node goes into the Bus-Off state when the TEC is greater than 255 (receive errors cannot cause a node to go Bus-Off). This means that a faulty node will be turned off if it transmits 32 consecutive messages with errors. In this mode, the node cannot send or receive messages, acknowledge messages, or transmit Error Frames of any kind. This is how Fault Confinement is achieved. There is a bus recovery sequence that is defined by the CAN protocol that allows a node in a Bus-Off state to recover, return to Error-Active, and begin 64
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- Page 39 and 40: 2.3.3 Synthesizable 1 - Wire® Bus
- Page 41 and 42: Figure 2.7 UART/RS232 Serial Port I
- Page 43 and 44: hardware. Through control registers
- Page 45 and 46: Table 2.2 1 - Wire® Bus Operations
- Page 47 and 48: 2.3.6 1 - Wire® Search Algorithm F
- Page 49 and 50: detected. This ‘read two bits’
- Page 51 and 52: in Figure 2.15. Alternatively, the
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- Page 55 and 56: 2.4.2 Device Functions and Typical
- Page 57 and 58: and development (R&D) investments b
- Page 59 and 60: 2.5 Network Types and Precedents As
- Page 61 and 62: 2.5.2 1 - Wire® Network Topologies
- Page 63 and 64: 2.5.3 1 - Wire® Network Limitation
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- Page 71 and 72: ecessive bit and the monitored stat
- Page 73 and 74: specification: Start-Of-Frame, Arbi
- Page 75 and 76: Cyclic Redundancy Check (CRC) Field
- Page 77 and 78: Arbitration FieldThe Arbitration Fi
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- Page 85 and 86: error occurs, an Error Frame is gen
- Page 87: Table 3.4 Error Flag Output Timing
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- Page 93 and 94: Figure 3.12 Propagation Delay Betwe
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- Page 101 and 102: CHAPTER 4 THE CHALLENGES OF INTERFA
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3.5.2 Error-Passive<br />
A node becomes Error-Passive when either the TEC or REC is equal to or greater than<br />
127. Error-Passive nodes are not permitted to transmit Active-Error Flags on the bus, but<br />
instead, transmit Passive-Error Flags which consist of six recessive bits. If the Error-Passive<br />
node is currently the only transmitter on the bus, then the passive error flag will violate the bit<br />
stuffing rule and the receiving node(s) will respond with Error Flags of their own (either active<br />
or passive depending upon their own error state). If the Error-Passive node in question is not the<br />
only transmitter (i.e. during arbitration) or is a receiver, then the Passive-Error Flag will have no<br />
effect on the bus due to the recessive nature of the error flag. When an Error-Passive node<br />
transmits a Passive-Error Flag and detects a dominant bit, it must see the bus as being idle for<br />
eight additional bit times after an intermission before recognizing the bus as available. After this<br />
time, it will attempt to retransmit. These measures restrict nodes that have a higher than average<br />
error rate so that they can’t interfere with communication across the bus.<br />
3.5.3 Bus-Off<br />
A node goes into the Bus-Off state when the TEC is greater than 255 (receive errors<br />
cannot cause a node to go Bus-Off). This means that a faulty node will be turned off if it<br />
transmits 32 consecutive messages with errors. In this mode, the node cannot send or receive<br />
messages, acknowledge messages, or transmit Error Frames of any kind. This is how Fault<br />
Confinement is achieved. There is a bus recovery sequence that is defined by the CAN<br />
protocol that allows a node in a Bus-Off state to recover, return to Error-Active, and begin<br />
64
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