Embedded Systems Design, 2nd Edition

Basic peripherals 133

It may be used as a chip select for the memory design or

simply as an I/O pin. The function that the pin performs is set up

internally through the use of a function register which internally

configures how the external pin is connected internally. If this is

not set up correctly, then despite the correct programming of the

other registers, the pin will not function as expected.

Note: This shared use does pose a problem for designers in

that many manufacturer data sheets will specify the total number

of I/O pins that are available. In practice, this is often reduced

because pins need to be assigned as chip selects and to other

essential ...