8085 program to subtract two 8-bit numbers with or without borrow

In this program we will see how to subtract two 8-bit numbers using 8085 microprocessor.

Problem Statement

Write 8085 Assembly language program to subtract two 8-bit numbers with or without borrow and store the result at locations 8050H and 8051H.

Discussion

In 8085, the SUB instruction is used 2’s complemented method for subtraction. When the first operand is larger, the result will be positive. It will not enable the carry flag after completing the subtraction. When the result is negative, then the result will be in 2’s complemented form and carry flag will be enabled.

We are using two numbers at location 8000H and 8001H. When the numbers are 78H and 5DH, then the result will be (78 – 5D = 1B) and when the numbers are 23H and CFH, then the result will be (23 – CF = 154) Here 1 indicates the number is negative. The actual result is 54H. It is in 2’s complemented form.

Input

first output

Address Data
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.
.
 .
.
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8000 78
8001 5D
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.
.
 .
.
.

second output

Address Data
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.
.
 .
.
.
8000 23
8001 CF
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.
.
 .
.
.

Flow Diagram

Address HEXCodes Labels Mnemonics Comments
F000 0E, 00
MVI C,00H Clear C register
F002 21, 00, 80
LXI H,8000H Load initial address to get operand
F005 7E
MOV A,M Load Acc with memory element
F006 23
INX H Point to next location
F007 46
MOV B, M Load B with second operand
F008 90
SUB B Subtract B from A
F009 D2, 0D, F0
JNC STORE When CY = 0, go to STORE
F00C 0C
INR C Increase C by 1
F00D 21, 50, 80 STORE LXI H,8050H Load the destination address
F010 77
MOV M, A Store the result
F011 23
INX H Point to next location
F012 71
MOV M, C Store the borrow
F013 76
HLT Terminate the program

Output

first output

Address Data
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.
.
 .
.
.
8050 1B
8051 00
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.
.
 .
.
.

second output

Address Data
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.
.
 .
.
.
8050 54
8051 01
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.
.
 .
.
.
Updated on: 2019-07-30T22:30:24+05:30

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