How to determine or control what part of the message is used in the CRC calculations?

The square [ ] brackets must be used to determine what part or parts of a message are used to calculate the CRC.  If you don't have [ ] brackets in your message then the CRC will always fail to calculate correctly.  If you need the whole message to be used then the whole message must be inside the brackets.  If you only want the CRC to be calculated between the stop and start bits then you need to put the brackets after the start bit and before the stop bit.