I am not familiar with the assembler you are using (WR REG P3.6), but I cannot imagine one that allow you to move a register into a bit (MOV WR,A). At WRITE for instance, you could save WR in C which is the only "bit register' in the '51. mov p3.6,C is a legal working instruction. I applaud you using symbolic names for the bits, but REG?, check your assembler manual.
Is this your first venture?
Have fun,
Erik