8085 Microprocessor Logical Instructions

YASH PAL,

8085 Microprocessor Logical Instructions – Logic instructions perform logic operations such as AND, OR, Exclusive-OR, NOT, rotate, and compare on the data of registers, memory locations, and immediate data. All logical instructions have one operand in the accumulator. The result is also stored in the accumulator.

Logical Instructions of 8085 Microprocessor

  1. ANDing Operations
  2. ORing Operations
  3. Ex-ORing Operations
  4. Complement Operation
  5. Compare Operations
  6. Rotate Operations

ANDing Operations

ANA RLogically AND the contents of the accumulator with the contents of register R.
OperationA ← A AND R
Length1 byte
Addressing modeRegister addressing mode
FlagsAll flags are affected with CY = 0 and AC = 1.
ANA MLogically AND the contents of the accumulator with the contents of the memory location pointed by register pair HL.
OperationA ← A AND [HL]
Length1 byte
Addressing modeIndirect addressing mode
FlagsAll flags are affected with CY = 0 and AC = 1.
ANI data (8 bit)Logically AND the 8-bit immediate data with the contents of the accumulator.
OperationA AND data
Length2 byte
Addressing modeImmediate addressing mode
FlagsAll flags are affected with CY = 0 and AC = 1.

ORing Operations

ORA RLogically OR the contents of the accumulator with the contents of register R.
OperationA ← A OR R
Length1 byte
Addressing modeRegister addressing mode
FlagsAll flags are affected according to the result with CY = 0 and AC = 1.
ORA MLogically OR the contents of the accumulator with the contents of the memory location pointed by register pair HL.
OperationA ← A OR [HL]
Length1 byte
Addressing modeIndirect addressing mode
FlagsAll flags are affected according to the result with CY = 0 and AC = 1.
ORI data (8-bit)Logically OR the contents of the accumulator with the immediate 8-bit data.
OperationA ← A OR data
Length2 byte
Addressing modeImmediate addressing mode
FlagsAll flags are affected according to the result with CY = 0 and AC = 1.

Ex-ORing Operations

XRA RLogically EX-OR the contents of register R with the accumulator contents. The result is stored in the accumulator.
OperationA ← A ExOR R
Length1 byte
Addressing modeRegister addressing mode
FlagsAll flags are affected according to the result with CY = 0 and AC = 1.
XRA MLogically EX-OR the contents of the memory location pointed by the HL register pair with the accumulator contents. The result is stored in the accumulator.
OperationA ← A ExOR [HL]
Length1 byte
Addressing modeIndirect addressing mode
FlagsAll flags are affected according to the result with CY = 0 and AC = 1.
XRI data (8-bit)Logically EX-OR the 8-bit immediate data with the accumulator contents and store the result in the accumulator.
OperationA ← A ExOR data
Length2 byte
Addressing modeImmediate addressing mode
FlagsAll flags are affected according to the result with CY = 0 and AC = 1.

Complement Operation

CMAComplement the contents of the accumulator.
OperationA ← A
Length1 byte
Addressing modeImplicit addressing mode
FlagsNo flag is affected.

Compare Operations

CMP RCompare (subtract) the contents of register R with the contents of the accumulator. The result of the subtraction operation is not stored.
OperationA – R
Length1 byte
Addressing modeRegister addressing mode
FlagsAll flags are affected according to the result. The result of the comparison can be obtained with the help of flags as follows:
A > R if CY = 0, Z = 0
A = R if CY = 0, Z = 1
A < R if CY = 1, Z = 0
CMP MCompare (subtract) the contents of the memory location pointed by register pair HL with the contents of the accumulator. The result is not stored.
OperationA – [HL]
Length1 byte
Addressing modeIndirect addressing mode
FlagsAll flags are affected according to the result. The result of the comparison can be obtained with the help of flags as follows:
A > M if CY = 0, Z = 0
A = M if CY = 0, Z = 1
A < M if CY = 1, Z = 0
CPI data (8 bit)Compare (subtract) the immediate data with the contents of the accumulator. The result is not stored.
OperationA – data
Length2 byte
Addressing modeImmediate addressing mode
FlagsAll flags are affected according to the result. The result of the comparison can be obtained with the help of flags as follows:
A > data if CY = 0, Z = 0
A = data if CY = 0, Z = 1
A < data if CY = 1, Z = 0

Rotate Operations

RLC rotate operation
Figure 1: RLC operation
RLCRotate the accumulator left without carry
OperationAs shown in the above image
Length1 byte
Addressing modeImplicit addressing mode
FlagsOnly the CY flag is affected according to the most significant bit (D7).
RAL rotate operation
Figure 2: RAL Operation
RALRotate the accumulator left with carry
OperationAs shown in the above image
Length1 byte
Addressing modeImplicit addressing mode
FlagsOnly the CY flag is affected according to the most significant bit (D7).
RRC rotate operation
Figure 3: RRC Operation
RRCRotate the accumulator right without carry
OperationAs shown in the above image
Length1 byte
Addressing modeImplicit addressing mode
FlagsOnly the CY flag is affected according to the most significant bit (D0).
RAR rotate operation
Figure 4: RAR Operation
RRCRotate the accumulator right with carry
OperationAs shown in the above image
Length1 byte
Addressing modeImplicit addressing mode
FlagsOnly the CY flag is affected according to the least significant bit (D0).

Note: The rotate instructions are primarily used in arithmetic multiply and divide operations and for serial data transfer.

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