Well, in case of long intergers or float numbers its best to pass the paramter by reference. But most of the times its just a byte of date to pass, can do with passing by value.

Another aspect of C is all parameters are passed on stack, as far as possible see if your compiler supports register paramter passing, it will save you some stack as well as some cycles.

Bottomline: it depends on the situation, and the type of data to be passed.

gary

P.S. Some newer MCS-51 variants support more than 256 bytes of internal memory, address wont be 1 byte in this case, so if the parameter is 8 bit, do it by value.

gary