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MCP2515-I/ST 参数 Datasheet PDF下载

MCP2515-I/ST图片预览
型号: MCP2515-I/ST
PDF下载: 下载PDF文件 查看货源
内容描述: 独立CAN控制器,SPI ™接口 [Stand-Alone CAN Controller With SPI⑩ Interface]
分类和应用: 控制器
文件页数/大小: 84 页 / 993 K
品牌: MICROCHIP [ MICROCHIP ]
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MCP2515  
2.4.1  
ACTIVE ERRORS  
2.5  
Overload Frame  
If an error-active node detects a bus error, the node  
interrupts transmission of the current message by  
generating an active error flag. The active error flag is  
composed of six consecutive dominant bits. This bit  
sequence actively violates the bit-stuffing rule. All other  
stations recognize the resulting bit-stuffing error and, in  
turn, generate error frames themselves, called error  
echo flags.  
An overload frame, shown in Figure 2-5, has the same  
format as an active error frame. An overload frame,  
however, can only be generated during an interframe  
space. In this way, an overload frame can be differen-  
tiated from an error frame (an error frame is sent during  
the transmission of a message). The overload frame  
consists of two fields: an overload flag followed by an  
overload delimiter. The overload flag consists of six  
dominant bits followed by overload flags generated by  
other nodes (and, as for an active error flag, giving a  
maximum of twelve dominant bits). The overload  
delimiter consists of eight recessive bits. An overload  
frame can be generated by a node as a result of two  
conditions:  
The error flag field, therefore, consists of between six  
and twelve consecutive dominant bits (generated by  
one or more nodes). The error delimiter field (eight  
recessive bits) completes the error frame. Upon  
completion of the error frame, bus activity returns to  
normal and the interrupted node attempts to resend the  
aborted message.  
1. The node detects a dominant bit during the  
interframe space, an illegal condition.  
Exception: The dominant bit is detected during  
the third bit of IFS. In this case, the receivers will  
interpret this as a SOF.  
Note:  
Error echo flags typically occur when a  
localized disturbance causes one or more  
(but not all) nodes to send an error flag.  
The remaining nodes generate error flags  
in response (echo) to the original error  
flag.  
2. Due to internal conditions, the node is not yet  
able to begin reception of the next message. A  
node may generate  
a maximum of two  
sequential overload frames to delay the start of  
the next message.  
2.4.2  
PASSIVE ERRORS  
If an error-passive node detects a bus error, the node  
transmits an error-passive flag followed by the error  
delimiter field. The error-passive flag consists of six  
consecutive recessive bits. The error frame for an error-  
passive node consists of 14 recessive bits. From this it  
follows that, unless the bus error is detected by an error-  
active node or the transmitting node, the message will  
continue transmission because the error-passive flag  
does not interfere with the bus.  
Note:  
Case 2 should never occur with the  
MCP2515 due to very short internal  
delays.  
2.6  
Interframe Space  
The interframe space separates a preceding frame (of  
any type) from a subsequent data or remote frame.  
The interframe space is composed of at least three  
recessive bits called the Intermission. This allows  
nodes time for internal processing before the start of  
the next message frame. After the intermission, the  
bus line remains in the recessive state (bus idle) until  
the next transmission starts.  
If the transmitting node generates an error-passive flag,  
it will cause other nodes to generate error frames due  
to the resulting bit-stuffing violation. After transmission  
of an error frame, an error-passive node must wait for  
six consecutive recessive bits on the bus before  
attempting to rejoin bus communications.  
The error delimiter consists of eight recessive bits and  
allows the bus nodes to restart bus communications  
cleanly after an error has occurred.  
DS21801D-page 8  
Preliminary  
© 2005 Microchip Technology Inc.  
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