In the "options for target" dialog box on the "Target" tab (uVision IDE) there is a check box called "Use On-chip XRAM...". When looking at the help file for this it says:
Use On-chip XRAM (0x0-0x2FF) Specifies the usage of the on-chip components that are typically enabled in the CPU startup code. If you are using on-chip xdata ram (XRAM) you should also enable the XRAM access in the startup file.
This sounds to me like I need to check this box and modify the 'start900.A51' startup file to get the on chip xdata to work. Is my assumption correct? What exactly does 'Checking' this box do?