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I/O Port

The following configuration settings are required when additional address lines are connected to I/O Port lines (?B_MODE = 0).

Name Description
?B_PORT Used to specify the address of the internal data port. The SFR address of an internal data port must be specified. (For example: P1 as for port 1).
?B_FIRSTBIT Indicates which bit of the 8051 I/O port is to be assigned first. The value 3 indicates that port bit 3 is used as first port line for the address extension. If, for example, two address lines are used, P1.3 and P1.4 are allocated in this case. The remaining lines of the 8051 I/O port can be used for other purposes.
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