Canbus ID filter and mask

最新推荐文章于 2025-08-06 18:47:16 发布

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最新推荐文章于 2025-08-06 18:47:16 发布

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CAN总线是一种无冲突的两线半双工总线系统，所有节点接收所有广播数据并判断是否相关。通过接受过滤器和屏蔽值，硬件实现对不需要的消息进行过滤。过滤器和屏蔽值用于决定接收到的帧标识符中哪些位需要比较。如果屏蔽位为0，则对应的ID位自动接受；如果屏蔽位为1，只有当该位与过滤器位匹配时才接受帧。通过设置不同的过滤器和屏蔽值，可以实现不同范围的帧ID接受策略。

Canbus ID filter and mask

CANBUS is a two-wire, half-duplex, bus based LAN system that is ‘collision free’.

Data is BROADCAST onto the bus -THERE IS NO SUCH THNG AS A POINT TO POINT CONNECTION as with data LANs.

All nodes receive all broadcast data and decide whether or not that data is relevant.

A CANBUS B frame consists of a four byte header (containing a 29-bit identifier), followed by up to 8 data bytes.

A receiving node would examine the identifier to decide if it was relevant (e.g. waiting for a frame with ID 00001567 which contains data to switch on or off a motor).

It could do this via software (using a C if or case statement); in practice the Canbus interface contains firmware to carry out this task

using the acceptance filter and mask value to filter out unwanted messages.

The filter mask is used to determine which bits in the identifier of the received frame are compared with the filter

If a mask bit is set to a zero, the corresponding ID bit will automatically be accepted, regardless of the value of the filter bit.
If a mask bit is set to a one, the corresponding ID bit will be compare with the value of the filter bit;
if they match it is accepted otherwise the frame is rejected.