Programming example of serial port dynamic scanning display circuit-EEWORLD

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The number of parallel I/O ports of a single-chip microcomputer is always limited. Sometimes the parallel ports need to be used for other more important purposes. Generally, a large number of parallel I/O ports are not used exclusively to drive display circuits. Can the serial communication port of 80C51 plus a small amount of I/O and expansion chips be used for display circuits? The answer is yes.

The serial communication port of 80C51 is a powerful communication port, and it is quite easy to use. It is very suitable for display driver circuit. Now we design a 4-bit LED display circuit based on this need by using two serial communication port lines plus two ordinary I/O ports. Of course, as long as two more I/O port lines are added, an 8-bit LED display circuit can be easily realized.

Serial port dynamic scanning display circuit programming example - Blue Sky Eagle - Blue Sky Eagle's Blog

The left picture is the electrical schematic. We still use the C2051 microcontroller, and use the cheap and easily available 74LS164 and 74LS138 as expansion chips. The 74LS164 (detailed technical manual) is an 8-bit serial-input and parallel-output shift register. Its function here is to decode the serial data output by the C2051 serial communication port and output it on its parallel port line, thereby driving the LED digital tube. The 74LS138 is a 3-8 decoder, which decodes the address signal output by the microcontroller and dynamically drives the corresponding LED. However, the current driving capacity of the 74LS138 is relatively small, so we use the final drive transistor 2SA1015 as the address driver.

Connect the segments of the four LEDs together, and their common ends are time-selected by 74LS138, so that at any time, only one LED is lit, which is the dynamic scanning display mode. Its advantages have been explained in the previous section. Using the serial port for LED communication, the program writing is quite simple. The user only needs to send the data to be displayed directly to the serial port send buffer and wait for the serial interrupt. Take a look at the following program.

Program List

Reference address：Programming example of serial port dynamic scanning display circuit

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