The document discusses various arithmetic operations that can be performed by the 8085 microprocessor such as addition, subtraction, incrementing and decrementing. It provides details on the mnemonics used to perform each operation and how operands are added or subtracted from the accumulator register. Instructions like ADD, SUB, INR and DCR are used to perform basic arithmetic on registers or memory locations, while ADI, SUI allow operating with immediate data. ADC, SBB consider the carry flag, and DAD performs 16-bit addition of register pairs.

1. B.RAMA PRABHA
ASSISTANT PROFESSOR,
DEPARTMENT OF COMPUTER SCIENCE,
K.C.S.KASI NADAR COLLEGE OF ARTS & SCIENCE,
CHENNAI-21

2. ARITHMETIC OPERATIONS
The 8085 microprocessor performs various arithmetic operations such as addition,
subtraction, increment and decrement operations. These arithmetic operations have the
following mnemonics.
 ADD – Add (Add the content of a register)
 ADI – Add Immediate (Add 8 bit data)
 SUB – Subtract (Subtract the content of a register)
 SUI – Subtract Immediate (subtract 8 bit data)
 INR – Increment (Increase the content of register by 1)
 DCR – Decrement(Decrease the content of register by 1)
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3. Addition in 8085
 Any 8-bit value, or the contents of any register, or even the contents of a
memory location pointed by HL pair, can be summed up with the
contents of the accumulator register.
 The added value, i.e., the result is then stored in the accumulator register
itself.
 This function cannot be be used for two other registers together – the
addition has to be performed with the accumulator being one of the
addends.
 Thus, for example, the contents of, say, register C cannot be summed up
directly to the contents of register B.
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4. ADD
 This is a 1 byte instruction.
 As discussed earlier, the contents of any register or memory location are added to the
contents of the accumulator register. The corresponding sum is then saved in the
accumulator. If the second addend is a memory, its address is specified by the H-L pair. All
flags linked with the addition are updated with the result of the addition performed.
Example : ADD B
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The Opcode The Operand Description
ADD
R
Add register to the
accumulator
M
Add contents from the
location pointed by the HL
pair (M) to the contents of the
accumulator

5. ADC(ADD WITH CARRY)
 This is a 1 byte instruction.
 The only difference between the ADD and the ADC operations is that the ADC condition
considers the carry value as well. Thus, the Carry flag plays an important role and becomes
the third addend..
Example : ADC B
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The Opcode The Operand Description
ADC
R
Add register to the
accumulator with carry
M
Add the content of the
location pointed by the value
in the HL pair (M) to the
accumulator with carry.

6. ADI(ADD IMMEDIATE WITH DATA)
 This is a 2 byte instruction.
 The contents of the accumulator register are added with immediate 8-bit data using the ADI
instruction. The sum is thus stored in the accumulator. All flags are correspondingly
modified...
Example : ADI 05H
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The Opcode The Operand Description
ADI 8-bit immediate data
Add immediate value to the
accumulator
[A] <- [A] + data

7. DAD(ADD 16 BIT DATA)
 This is a 2 byte instruction.
 The 16-bit contents of any 8085 register pair are added to the contents of the H-L register
pair. The result is also stored in the H-L pair. The carry flag is also updated with the result of
the addition operation. No other flag bits are affected.
Example : DAD B
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The Opcode The Operand Description
DAD Register pair
Add contents of register pair
to contents of H-L pair. The
result is stored in the H-L
pair.

8. Subtraction in 8085
 Any 8-bit value, or the contents of any register, or even the contents of a
memory location can be subtracted from the contents of the accumulator
register.
 The difference of this operation is stored in the accumulator.
 The subtraction is performed in 2’s complement form. (You can revisit
the concept of 2’s complement over here.)
 Also, if the result of the subtraction is negative, it is stored in its 2’s
complement form.
 Similar to the addition operation, no two 8-bit registers can be subtracted
directly, unless it is subtracted from the accumulator.
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9. SUB(SUBTRACT TO THE REGISTER)
 This is a 1 byte instruction.
 The contents of any register or memory location are subtracted from the contents of the
accumulator register. The corresponding difference is then saved in the accumulator register.
If the operand is a memory, its address is specified by the H-L pair. All flags linked with the
subtraction operation are updated with the result of the operation performed.
Example : SUB B
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The Opcode The Operand Description
SUB
R
Subtract register from the
accumulator
M
Subtract contents of the
location pointed by HL pair
(M) from the accumulator

10. SBB(SUBTRACT TO THE REGISTER WITH BORROW)
 This is a 1 byte instruction.
 The contents of any register or memory location AND the borrow value (the CY flag in this
case) are subtracted from the contents of the accumulator register. The corresponding
difference is saved in the accumulator register. If the operand is a memory, its address is
specified by the H-L pair.
Example : SBB B
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The Opcode The Operand Description
SBB
R
Subtract register from the
accumulator with borrow
considered
M
Subtract the contents of the
location pointed by the HL
pair (M) from the accumulator
with borrow considered

11. SUI(SUBTRACT IMMEDIATE WITH DATA)
 This is a 2 byte instruction.
 The contents of the accumulator register are subtracted with immediate 8-bit data using the
SUI instruction. The answer is thus stored in the accumulator. All flags are correspondingly
modified to reflect the difference
Example : SUI 04H
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The Opcode The Operand Description
SUI 8-bit immediate data
Subtract an immediate value
from the accumulator

12. SBI(SUBTRACT IMMEDIATE WITH BORROW)
 This is a 2 byte instruction.
 The contents of the accumulator register are subtracted with immediate 8-bit data AND the
borrow value (specified by the CY flag) using the SBI instruction. The answer is thus stored
in the accumulator. All flags are correspondingly modified to reflect the difference.
Example : SBI 04H
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The Opcode The Operand Description
SBI 8-bit immediate data
Subtract an immediate value
from the accumulator with
Borrow considered

13. SBI(SUBTRACT IMMEDIATE WITH BORROW)
 This is a 2 byte instruction.
 The contents of the accumulator register are subtracted with immediate 8-bit data AND the
borrow value (specified by the CY flag) using the SBI instruction. The answer is thus stored
in the accumulator. All flags are correspondingly modified to reflect the difference.
Example : SBI 04H
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The Opcode The Operand Description
SBI 8-bit immediate data
Subtract an immediate value
from the accumulator with
Borrow considered

14. Increment or Decrement in 8085
 Every register or memory location holds contents of size 8-bits. These
contents can be incremented and/or decremented by a value of 1.
 If we consider register pairs, then the 16-bit contents can also be
incremented or decremented by a value of 1.
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15. INR(INCREMENT BY 1)
 This is a 1 byte instruction.
 The INR command is used to increment/increase the contents of a register or of the data at
the location pointed by HL pair(M) by one. The result is stored in the same location itself. In
the case of the operand being M, the value at the memory location given by the HL pair is
incremented by one. The value in the HL register pair does not change.
Example : INR B ,INR 1250M
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The Opcode The Operand Description
INR
R
Increment Register contents
by one
M
Increment the content at the
memory location pointed by
the HL pair by one

16. INX(INCREMENT REGISTER PAIR BY 1)
 This is a 1 byte instruction.
 The INX instruction increments the contents of a register-pair by the value of one. The result
is stored in the same place itself.
Example : INX H
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The Opcode The Operand Description
INX R
Increment contents of register
pair by one

17. DCR(DECREMENT BY 1)
 This is a 1 byte instruction.
 The DCR command is used to decrement/decrease the contents of a register or of a memory
location by the value of one. The result after this operation is stored in the same location
itself. If the operand happens to be a memory location, its address is then specified by the
contents of the H-L pair.
Example : DCR B , DCR 1250M
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The Opcode The Operand Description
DCR
R
Decrement Register contents
by one
M
Decrement the content at the
memory location pointed by
the HL pair by one

18. DCX(DECREMENT REGISTER PAIR BY 1)
 This is a 1 byte instruction.
 The DCX instruction decrements the contents of the register-pair by the value of one. The
result is stored in the same place itself.
Example : DCX H
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The Opcode The Operand Description
DCX R
Decrement register pair by
one

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