How to analyze this sentence?

[Andy Lin]

During a slave receive transfer, after the device has identified the protocol and command must accept and check the additional PEC for validity.

I want to split it out into three sentence, two dependent clauses and one independent clause.

Because "after" and "and" are conj, the whole sentence can be split into three sentence.

The independent clause is : command must accept and check the additional PEC for validity.
The dependent clauses are : after the device has identified the protocol during a slave receive transfer.

Question 1: In the independent clause, what is the object of command?(command must accept what?)
Question 2: Why I only can split it into two sentence, where is the third sentence? Or the "after" is not the conj?

 

[Andy Lin]

To Piscean:

Hi, thank you replying me. May I ask why the final clause would be an independent clause after revised?
Second, I read from the English textbook, it says: There is must a independent in the sentences, why here is no independent?