DTU 数据接收前导字校验代码解析

This code is for receiving data from a DTU (Data Terminal Unit) device. The DTU sends data in a specific format with a preamble consisting of three bytes: 0x55, 0xFD, and 0xAA. The code checks if the received data matches this preamble before proceeding to receive the actual data.

The variable 'DTU_Pre_Received' is used to track if the preamble has been received successfully. The variable 'DTU_Pre_Num' is used to track the number of bytes in the preamble that have been received so far. The variable 'DTU_Rx_Data' is used to store the received byte.

If 'DTU_Pre_Received' is 0, the code checks if the received byte matches the first byte of the preamble (0x55). If it does, then 'DTU_Pre_Num' is incremented. If it doesn't match, the code checks if 'DTU_Pre_Num' is 1 and if the received byte matches the second byte of the preamble (0xFD). If it does, then 'DTU_Pre_Num' is incremented again. If it doesn't match, the code checks if 'DTU_Pre_Num' is 2 and if the received byte matches the third byte of the preamble (0xAA). If it does, then the preamble has been received successfully and 'DTU_Pre_Received' is set to 1. 'DTU_Rx_Data_Count' is also reset to 0 to start receiving the actual data.

If the received byte doesn't match any of the expected bytes in the preamble, then the preamble reception has failed and the code resets the variables and returns without processing the received data.