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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  
identifier is compared to the masks and filters to deter-  
mine if the message should be loaded into a receive  
buffer. The mask essentially determines which bits to  
apply the acceptance filters to. If any mask bit is set to  
a zero, that bit will automatically be accepted,  
regardless of the filter bit.  
4.5  
Message Acceptance Filters and  
Masks  
The message acceptance filters and masks are used to  
determine if a message in the message assembly  
buffer should be loaded into either of the receive  
buffers (see Figure 4-5). Once a valid message has  
been received into the MAB, the identifier fields of the  
message are compared to the filter values. If there is a  
match, that message will be loaded into the appropriate  
receive buffer.  
TABLE 4-2:  
FILTER/MASK TRUTH TABLE  
Message  
Identifier  
bit  
Accept or  
Reject bit  
n
Mask Bit  
n
Filter Bit n  
0
1
1
1
1
X
0
0
1
1
X
0
1
0
1
Accept  
Accept  
Reject  
Reject  
Accept  
4.5.1  
DATA BYTE FILTERING  
When receiving standard data frames (11-bit identifier),  
the MCP2515 automatically applies 16 bits of masks  
and filters normally associated with extended  
identifiers to the first 16 bits of the data field (data bytes  
0 and 1). Figure 4-4 illustrates how masks and filters  
apply to extended and standard data frames.  
Note:  
X= don’t care  
Data byte filtering reduces the load on the MCU when  
implementing Higher Layer Protocols (HLPs) that filter  
on the first data byte (e.g., DeviceNet™).  
As shown in the receive buffers block diagram  
(Figure 4-2), acceptance filters RXF0 and RXF1 (and  
filter mask RXM0) are associated with RXB0. Filters  
RXF2, RXF3, RXF4, RXF5 and mask RXM1 are  
associated with RXB1.  
4.5.2  
FILTER MATCHING  
The filter masks (see Register 4-14 through  
Register 4-17) are used to determine which bits in the  
identifier are examined with the filters. A truth table is  
shown in Table 4-2 that indicates how each bit in the  
FIGURE 4-4:  
MASKS AND FILTERS APPLY TO CAN FRAMES  
Extended Frame  
ID10  
ID0 EID17  
EID0  
Masks and Filters apply to the entire 29-bit ID field  
Standard Data Frame  
ID10  
ID0 *  
Data Byte 0  
Data Byte 1  
11-bit ID Standard frame  
16-bit data filtering *  
* The two MSb (EID17 and EID16) mask and filter bits are not used.  
DS21801D-page 32  
Preliminary  
© 2005 Microchip Technology Inc.  
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