The result will be the address of label DB 3FH (line15) and the data present in this address ie 3FH (digit drive pattern for 0) gets moved into the accumulator. Execution of MOVC will add oooo1001B to the content in PC ( address of next instruction). After this the program resumes from the line after MOVC the program, initial value in A is 00001001B. Execution of this instruction will add the value in the accumulator A with the content of the program counter(address of the next instruction) and will move the data present in the resultant address to A. Instruction MOVC is the instruction that produces the required digit drive pattern for the display. Done to check if counting has been finished.ĭELAY: MOV R4,#05H // subroutine for delay JZ START //Checks accumulator for zero and jumps to START. MOV A,R0 // R0 moved to accumulator to check if it is zero in next instruction. MOVC // adds the byte in A to the program counters addressĪCALL DELAY // calls the delay of the timer MOV R0,#0AH //Register R0 initialized as counter which counts from 10 to 0 START: MOV A,#00001001B // initial value of accumulator Put the current digit drive pattern into a port for displaying.Īll the above said tasks are accomplished by the program given below.Convert the current count into digit drive pattern.Form a 0 to 9 counter with a predetermined delay (around 1/2 second here).The software part of the project has to do the following tasks. C1, C2 and X1 are related to the clock circuit. S3 is the reset switch and R2,C3 forms a debouncing circuitry. R3 to R10 are current limiting resistors. The common cathode seven segment display D1 is connected to the Port 1 of the microcontroller (AT89S51) as shown in the circuit diagram. How to setup simple 0 to 9 up counter using 8051 and more importantly how to interface a seven segment LED display to 8051 in order to display a particular result. This simple circuit illustrates two things. The circuit diagram shown above is of an AT89S51 microcontroller based 0 to 9 counter which has a 7 segment LED display interfaced to it in order to display the count. Interfacing seven segment display to 8051. The common digit drive patterns (0 to 9) of a seven segment display are shown in the table below. 7 segment LED displayĭigit drive pattern of a seven segment LED display is simply the different logic combinations of its terminals ‘a’ to ‘h‘ in order to display different digits and characters. The pin out scheme and picture of a typical 7 segment LED display is shown in the image below. In common anode type, the anode of all LEDs are tied together as a single terminal and cathodes are left alone as individual pins. In common cathode type, the cathode of all LEDs are tied together to a single terminal which is usually labeled as ‘ com‘ and the anode of all LEDs are left alone as individual pins labeled as a, b, c, d, e, f, g & h (or dot). Seven segment displays are of two types, common cathode and common anode. Different characters can be displayed by selectively glowing the required LED segments. A seven segment display consists of seven LEDs arranged in the form of a squarish ‘8’ slightly inclined to the right and a single LED as the dot character. Knowledge about how to interface a seven segment display to a micro controller is very essential in designing embedded systems. 7 segment LED display is very popular and it can display digits from 0 to 9 and quite a few characters like A, b, C. This article is about how to interface a seven segment LED display to an 8051 microcontroller.
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