>     The data book states that BCF,BSF, etc are read modify write
> instructions and care has to be taken with using these instruction on a port
> - The question is, what is the 'etc' instructions they are on about.
> I can see that any instruction that is set to write back to 'f' where 'f' is
> a port, could come under this title, but are there any others??

Any instruction (other than MOVWF and CLRF) which writes to a port will read
it first and use the read value in computing what to write there.  While BSF
and BCF are the most common read/modify/write instructions used on port pins,
all instructions other than MOVWF which write the port pins will have the
same caveats.

Note, btw, that at least on the 16C84 (and probably on other members of the
16Cxx family) even the movwf and clrf instructions will read an address before
they write to it.  This is usually not a problem, but if an address has side-
effects on a read (such as the port B compare latches) those side-effects will
also be triggered on a write.