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When additional address lines are connected to XDATA-mapped port lines (?B_MODE = 1) the following configuration settings are required.

Name Description
?B_XDATAPORT Specifies the XDATA memory address used to select the bank address and defines the address of an external data port. Any XDATA address can be specified (address range 0H to 0FFFFH) under which a port can be addressed in the XDATA area. 0FFFFH is defined as the default value. In this mode, ?B_CURRENTBANK and ?B_XDATAPORT are initialized with the value 0 at the start of the program by the C51 startup code.
?B_FIRSTBIT Indicates which bit of the defined port is to be assigned first. Other than ?B_MODE=0, the remaining bits of the XDATA port cannot be used for other purposes.

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