SCM Parallel I / O port number is always limited, and sometimes parallel port be used for other more important purposes , generally will not use a large number of parallel I / O port designed to drive display circuit , can use the 80C51 Serial Communication port with a small amount of I / O and expansion of the circuit chip is used to display it ? The answer is yes. 80C51 serial communication port is a powerful communication port , and is very easy to use communication port , very appropriate for the display driver circuit , following on the basis of this we need to design a line with two serial communication port Plus 2 general I / O port , to design a 4-bit LED display circuit . Plus of course as long as two I / O port line can be easily achieved eight LED display circuit . I

n the circuit diagram, we use C2051 MCU, also with cheap easy to get the 74LS164 and 74LS138 chips as an extension . 74ls164 is an 8-bit serial shift register into and out of its functions here will C2051 serial port output of serial data decoding and output in the parallel line to drive LED digital tube . Decoder 74LS138 is a 3-8 , it will signal MCU address output after decoding the dynamic driving the corresponding LED. But the current drive capability 74LS138 smaller end, we used the non -driver transistor 2SA1015 drive as the address . Dan will be four LED 's are connected together by their common side 74LS138 time- gating , so that any one moment there is only one LED in the light , that is dynamic scan display , the advantage in the previous section We have described . LED serial port to communicate programming is quite simple , users simply need to display data directly sent to the serial port send buffer , you can wait for serial interrupt .