In C51 manual,the IDATA memory type is described as following: Indirectly addressable internal data memory; accessed across the full internal address space (256 bytes). But in file of STARTUP.a51,the default value of IDATALEN equals 80h,I wonder if it be FFh,and if my system is based on 8052, should IDATALEN be FFh? I am a freshman in C programing and need your help. Thanks a lot.