My team mate in robocup team has run out of memory space in the MCS51 microprocessor, but we still have the whole program of the PID algorithm to get the steady speed of the motors that run the omni-wheels. We consulted the distributors and the manual, but they only suggest us to use external memory device. With limited space in the robot circuit, we can't bear having more electronic device into it. So, we found "xregister" and used it without knowing what it is. The result turns out to be the inconsistance of robot responses, which we have no clue of the source. Has anybody heard of this "xregister" thing? Please advise