Selection of MCS-51 series AT89S51 microcontroller as microcontrollers, select two quadruple consisting of common cathode LED display module 8, due to the limited AT89S51 microcontroller drive capability, using two 74HC244 achieve bus driver, a 74HC244 done bit control line control and drive, another 74HC244 completed 7-segment digital tube output, the output port of each series with a 100 ohm resistor on the 7-segment current limiting.
As the number of small keyboard, select the connection as four separate buttons and keys to enter the P1 port. When no key is pressed P1.0-P1.3 is high, when a key is pressed, P1.0-P1.3 corresponding pin is low. Circuit diagram is shown below.
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