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AN APPLICATION OF 8085 REGISTER INTERFACING
WITH LED
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Presented By:-
Taha Malampattiwala 140050107052
CSE 1 [Batch 4]
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BASIC I/O CONCEPTS
• Peripherals such as LEDs and keypads are essential components of microcontroller-based systems
• Input devices• Provide digital information to an MPU
• Examples: switch, keyboard, scanner, and digital camera
• Output devices • Receive digital information from an MPU
• Examples: LED, seven-segment display, LCD, and printer
• Devices are interfaced to an MPU using I/O ports
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I/O INTERFACING
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INTERFACING AND ADDRESSING
• I/O ports
• Buffers and latches on the MCU chip
• Assigned binary addresses by decoding the address bus
• Generally bidirectional
• Internal data direction registers
• To read binary data from an input peripheral
• MPU places the address of an input port on the address bus
• Enables the input port by asserting the RD signal
• Reads data using the data bus
• To write binary data to an output peripheral
• MPU places the address of an output port on the address bus
• Places data on data bus
• Asserts the WR signal to enable the output port
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INTERFACING OUTPUT PERIPHERALS
• Commonly used output peripherals in embedded systems
• LEDs
• Seven-Segment Displays
• LCDs
• Two ways of connecting LEDs to I/O ports
• Common Cathode
• LED cathodes are grounded
• Logic 1 from the I/O port turns on the LEDs
• Current is supplied by the I/O port called current sourcing
• Common Anode
• LED anodes are connected to the power supply
• Logic 0 from the I/O port turns on the LEDs
• Current is received by the chip called current sinking
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SEVEN-SEGMENT DISPLAY
• Seven-segment Displays
• Used to display BCD digits
• 0 thru 9
• A group of 7 LEDs physically mounted in the shape of the number eight
• Plus a decimal point
• Each LED is called a segment
• ‘a’ through ‘g’
• Two types
• Common anode
• Common cathode
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SEVEN-SEGMENT DISPLAY
• Common Anode
• All anodes are connected together to a power supply
• Cathodes are connected to data lines
• Logic 0 turns on a segment
• Example: To display the digit 1
• All segments except b and c should be off
• 11111001 = F9H
9 330_09
Common Anode
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SEVEN-SEGMENT DISPLAY
• Common Cathode
• All cathodes are connected together to ground
• Anodes are connected to data lines
• Logic 1 turns on a segment
• Example: To display digit 1
• All segments except b and c should be off
• 00000110 = 06H
330_09
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INTERFACE AN 8-DIGIT 7 SEGMENT LED DISPLAY TO THE 8085 MICROPROCESSOR SYSTEM AND WRITE AN 8085 ASSEMBLY LANGUAGE ROUTINE TO DISPLAY MESSAGE ON THE DISPLAY.
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1. MVI A, 80H : Load control word in AL
2. OUT CR : Load control word in CR
3. MVI B, 08H : load count
4. MVI C, 7FH : load select pattern
5. LXI H, 6000B : starting address of message
6. DISP 1: MOV A, C : select digit
7. OUT PB
8. MOV A, M : get data
9. OUT PA : display data
10. CALL DELAY : wait for some time
11. DISP 1: MOV A, C
12. RRC
13. MOV C, A : adjust selection pattern
14. INX H
15. DCR B : Decrement count
16. JNZ DISP 1 : repeat 8 times
17. RET
18. Delay: LXI D, Count : Delay Subroutine
19. Back: DCX D
20. MOV A, D
21. ORA E
22. JNZ Back
23. RET
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