Open ShellAlbert opened 4 years ago
Process Data Objects (PDOs)
As mentioned earlier, we are using the Buffered mode for our data communications. The sync managers essentially provide a shared memory interface between a master and a slave. This great but it doesn't provide a way to define a communications protocol between a master and a slave.
This problem is solved by Process Data Objects (PDOs).
PDOs are a way of defining how data is packed into a buffered sync manager.
The use of a standardized PDO description (as described in the ESI file) make it possible for any EtherCAT master stack to communicate with any slave without large amounts of customization.
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Ethercat FMMU
FMMU的功能是将主站分配的逻辑地址转换为本地地址,每一个FMMU通道将一段连续的物理地址映射到一段连续的逻辑地址中。这样就实现了主站的逻辑寻址和实际物理地址的映射。
FMMU设置:
1、 主站读取每一个从站的硬件配置包括输入输出数据的长度。
2、 主站组织数据编址。
3、 主站将为每一个从站的分配好的逻辑地址下发到各个从站中(配置FMMU configuration register)。
4、 数据开始传输。
FMMU的配置工作由主站操作。对于从站的开发来说只需要核对好设备描述文件中的地址分配就可以了。