You should read Dallas Application note #27 Understanding and using cyclic redundancy checks.

You will need to select one of the three provided crc8 routines and put that in your PBP program. You call it as a subroutine. Each routine does the same thing but take different amounts of time/different amounts of programming space doing it. These routines operate on a byte at a time not a bit at a time. They do the bit calculations for you.

Receive one byte from the device or more likely, you will have to receive all bytes that are included in the crc check and place them in appropriate variables or an array. Make the variable CRCData = the first byte then do a gosub to the name of the CRC subroutine. Do the same thing for the second byte, third, etc. After all the bytes have been passed through the CRC routine then the variable CRC will contain the crc value that should match the one sent from the device.