INT E0 - PCROBOTS v1.41 - "REGISTER_X" - SELECT AUTOMATIC X POSITION UPDATES
	AX = 002Dh
	BX:CX -> X word variable
Return: AX = status (0001h OK, 0000h problem with address)
Note:	after this call, PCROBOTS will automatically update the specified
	  word whenever the robot moves
SeeAlso: AX=002Eh