First of all, thank you for answering my questions.
K66 single chip microcomputer as the control core,complete the collection of analog electric quantity and transfer the collection result through CAN and USB。Now there are the following questions:
1.How to improve the accuracy of AD acquisition? What is the relationship between sampling period and conversion time?Whether ADC accuracy can be improved by changing the configuration of conversion time register？
2.What is the reason that K66 can send data to PC, but can't receive the data sent by PC?
3.After downloading the program, connect the K66 control board and PC with USB. There is no device identification in the PC device manager. Why? During this time, the driver is replaced many times.
Thank you very much.
Since I can't see your code this is only a supposition, but you should avoid blocking code so any transfer can be done correctly, also as a recommendation, I will suggest using the DMA to handle the CAN transfers so this wouldn't interfere with the USB stack.
I think this is a software problem but if you have a FRDM-K66 maybe it is worth trying your same code to check if there isn't any hardware problem.
Usually, this is done when you write in the location 0x400 - 0x40C, usually in the linker file this section is reserved for the structure called Flash_Config in the startup code. If this section is modified is very likely your MCU will lock. Check the following link with some methods to unlock the board.