Philip, you don't need to change the whole port to i/p to read
Busy, just bit7. Here's an example that I've used forever. Maybe
you're having trouble because of the whole-port thing, but I'm
sure I've done that too and don't recall any problems

         bsf    rw            ;set up for Busy Flag read
         usec
         bcf    rs
         usec
         clrf   portb
         usec
         mov    b'10000000',trisb
         bsf    en
         usec

getbusy  btfsc  busy          ;loop until Busy Flag clear
         bra    getbusy

         bcf    en
         usec
         bcf    rw
         mov    b'00000000',trisb

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