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To configure general purpose I/O for an I/O chip, one needs to determine two things. One is the address of the configuration registers for setting the port functionality; the other is the address of the port. Some I/O chips provides extra registers to allow the user to enable or disable I/O ports, determine the power output of each I/O pin, etc.
To configure a serial port of an I/O chip, one usually needs to specify the bit rate (number of bits per second transmitted), number of bits per word (note that one word is transmitted at a time), and the synchronization signal between the sender and receiver. Some chips also provide registers to let the user specify the error checking format.