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Serial data input and output is more complex as timing has to be provided along with data and clear/enable signals. So for 8 inputs an overhead of 3 ports is required but 8 more inputs need no more ports as the I.C.s are concatenated and 16 shift clocks used to read them.
Serial output such as to LED's or LCD display again concatenates the shift registers so many outputs can be obtained from the 4 ports required to service them. Useful I.C.s are the 74HC595 shift register,
Serial data input and output is more complex as timing has to be provided along with data and clear/enable signals. So for 8 inputs an overhead of 3 ports is required but 8 more inputs need no more ports as the I.C.s are concatenated and 16 shift clocks used to read them.
Serial output such as to LED's or LCD display again concatenates the shift registers so many outputs can be obtained from the 4 ports required to service them. Useful I.C.s are the 74HC595 shift register,
LINK TO IMAGE - int-3.gif
Circuit Schematic
