I select a chip which has 512 BYTE RAM, but i only can watch the content of low 128 BYTE RAM. thanks for your help.
Please select the appropriate Product when making a post! I presume you're talking C51? Read the section "Internal Data Memory" in the manual (C51 User's Guide; C51.pdf). Manuals are accessible via the 'Books' tab in the uVision Project window.
Note that on the 8051 devices that "say" they have 512 or 1024 bytes of RAM, this is not an accurate statement. What they MEAN is that they have 256 bytes of DATA memory and 256 bytes of XDATA memory. The reason you can't view 512 bytes of DATA memory is because the address of DATA is limited to 8 bits (256 bytes). You'll just have to look at the memory the way it is implemented--as 2 separate memory areas. Take a look at the following knowledgebase article for more information: http://www.keil.com/support/docs/302.htm Jon