Code Conversion in 8085 Microprocessor
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This document discusses various code conversion techniques used in microprocessors, including binary to BCD, BCD to binary, hexadecimal to BCD, and conversions to ASCII and seven-segment displays. It provides examples of assembly language code to perform these conversions and explains the basic steps or logic involved, such as using positional weighting, repeated addition or subtraction, and lookup tables.
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Code Conversion in 8085 Microprocessor
- 1. MADE BY MOHIT AGARWAL – (161080107026) 5TH SEM COMPUTER
- 2. Code conversion allows user to translate a number that is representated using one coding system to other coding system. The code conversion involves operations like : 1) Binary to BCD 2) BCD to Binary 3) BCD to Hex 4) Hex to BCD 5) BCD to Seven Segment 6) Binary to ASCII 7) ASCII to Binary
- 3. The microprocessor understands the binary/hex number system. To convert BCD number into its binary equivalent we need to use the principle of positional weighting in a given number. EXAMPLE : (2 Digit BCD to Binary) 60 = 6 x 0A H + 0 60 = 3C H + 0 60 = 3C H
- 4. LDA 2200H : Get the BCD number MOV B, A : Save it ANI OFH : Mask most significant four bits MOV C, A : Save unpacked BCD 1 in C register MOV A, B : Get BCD again ANI FOH : Mask least significant four bits RRC : Convert most significant four bits into unpacked BCD 2 RRC RRC RRC MOV B, A : Save unpacked BCD 2 in B register XRA A : Clear accumulator (sum = 0) MVI D, 0AH : Set D as a multiplier of 10 SUM:ADD D : Add 10 until (B) = 0 DCR B : Decrement BCD2 by one JNZ SUM : Is multiplication complete? If not, go back and add again ADD C : Add BCD 1 STA 2300H : Store the result HLT : Terminate program execution INPUT : 2200 H : 60 H OUTPUT : 2300 H : 3C H
- 5. The microprocessor processes data in binary form but data that is displayed is in BCD form. Hence, we require to convert the Binary data to BCD. The series of operations to be performed is represented here using a flowchart.
- 6. Source Program: LXI SP, 27FFH : Initialize stack pointer LDA 6000H : Get the binary number in accumulator CALL SUBROUTINE : Call subroutine HLT : Terminate program execution Subroutine to convert binary number into its equivalent BCD number: PUSH B : Save BC register pair contents PUSH D : Save DE register pair contents MVI B, 64H : Load divisor decimal 100 in B register MVI C, 0AH : Load divisor decimal 10 in C register MVI D, 00H : Initialize Digit 1 MVI E, 00H : Initialize Digit 2
- 7. STEP1:CMP B : Check if number < Decimal 100 JC STEP 2 : if yes go to step 2 SUB B : Subtract decimal 100 INR E : update quotient JMP STEP 1 : go to step 1 STEP2:CMP C : Check if number < Decimal 10 JC STEP 3 : if yes go to step 3 SUB C : Subtract decimal 10 INR D : Update quotient JMP STEP 2 : Continue division by 10 STEP3:STA 6100H : Store Digit 0 MOV A, D : Get Digit 1 STA 6101H : Store Digit 1 MOV A, E : Get Digit 2 STA 6102H : Store Digit 2 POP D : Restore DE register pair POP B : Restore BC register pair RET : Return to main program INPUT : 3040 H : 8A H OUTPUT : 3041 H : 08 H 3042 H : 03 H 3043 H : 01 H
- 8. The ASCII (American Standard Code for Information Interchange) is used for communication purposes. Hence, it is necessary to convert Binary number to its ASCII equivalent.
- 9. Source program: LXI SP, 27FFH : Initialize stack pointer LXI H, 2000H : Source memory pointer LXI D, 2200H : Destination memory pointer MVI C, O5H : Initialize the counter BACK: MOV A, M : Get the number CALL ASCII : Call subroutine ASCII STAX D : Store result INX H : Increment source memory pointer INX D : Increment destination memory pointer DCR C : Decrement count by 1 CJNZ : If not zero, repeat HLT : Stop program execution a
- 10. Subroutine ASCII: ASCII:CPI, OAH : Check if number is OAR JNC NEXT : If yes go to next otherwise continue ADI 30H JMP LAST NEXT:ADI 37H LAST:RET : Return to main program INPUT : (2000H) = 1 (2001H) = 2 (2002H) = 9 (2003H) = A (2004H) = B OUTPUT : (2200H) = 31 (2201H) = 32 (2202H) = 39 (2203H) = 41 (2204H) = 42
- 11. Steps for ASCII to Binary code conversion : If ASCII code is less than 3A H then 30 H is subtracted from the number to get its Binary Equivalent. If the number is between 41 H and 5A H then 37 H is subtracted to get the binary equivalent of the letter A-F. EX: 41 H (ASCII) = 41 H - 37 H = 04 H (BINARY)
- 12. Steps for BCD to HEX code conversion : 1) We get the value from the user. 2) Then we take the Most Significant Digit (MSD). 3) We multiply MSD by 10, using repeated addition. 4) Then we add the Least Significant Digit (LSD) to the result obtained in previous step. 5) And finally the value is stored in the next memory location.
- 13. LXI H,0030H : Get the BCD number MOV A,M : Initialize the memory Pointer ADD A : Value in accumulator is doubled MOV B,A : Value in accumulator is moved to register B ADD A : Value in accumulator is doubled again ADD A : Value in accumulator is doubled again ADD B : Value in Register B is added to accumulator (A is 10 x MSD of the BCD stored at 0030H) INX H : Point to LSD ADD M : LSD is added to accumulator INX H Next location is pointed MOV M,A : Value obtained is stored here HLT : Terminate the program INPUT : 0030 H : 02 H 0031 H : 09 H OUTPUT : 0032 H : 1D H
- 14. Steps for HEX to BCD code conversion : 1) We get the HEX number from user. 2) Then shift the hexadecimal number to C register. 3) We perform repeated addition for C number of times. 4) And adjust for BCD count in each step. 5) Now the BCD value obtained is stored in memory.
- 15. LXI H,0030H : Get the HEX number MOV C,M : Shift the number to C register LOOP1: ADI 01H : Start a loop of repeated addition for C times DAA : Adjust for BCD count JNC LOOP2 : Start another loop for Higher order number INR D LOOP2: DCR C : Decrease C till it reaches Zero JNZ LOOP1 STA 0051H : Store the Lower order here MOV A,D : Move the Higher order value to accumulator STA 0050H : Store the Higher order here HLT INPUT : 0030 H : 1D H OUTPUT : 0050 H : 02 H 0051 H : 09 H
- 16. • The seven segment LCD display is used for displaying the results in a microprocessor based system. • In such cases we need to convert the results in the seven segment code. • Such conversion can be obtained with a look-up table. 0 3F 1 06 2 5B 3 4F 4 66 5 6D 6 7D 7 07 8 7F 9 6F
- 17. LXI H, 6200H : Initialize lookup table pointer LXI D, 6000H : Initialize source memory pointer LXI B, 7000H : Initialize destination memory pointer BACK: LDAX D : Get the number MOV L, A : A point to the 7-segment code MOV A, M : Get the 7-segment code STAX B : Store the result at destination memory location INX D : Increment source memory pointer INX B : Increment destination memory pointer MOV A, C CPI O5H : Check for last number JNZ BACK : If not repeat HLT : End of program
- 18. THANKYOU
Editor's Notes
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