CE - Basics -Flags

Select the ALU operation used by microprocessor to apply a bitwise mask to a register.

• AND with the mask

• XOR with 0xFF

• OR with 0x00

• ADD with the mask

Select the bus which carries the address of the next instruction from program counter (PC).

• Address bus

• Data bus

• Control bus

• Status flag lines

Calculate the final content of accumulator (A) and flag registers (S, Z, AC, P, CY) after the execution of the following assembly language program.

MVI A, FF H;

ANI 00 H;

• A = 00 H, S = 0, Z = 1, AC = 0, P = 1, CY = 0

• A = FF H, S = 1, Z = 1, AC = 0, P = 1, CY = 0

• A = F0 H, S = 0, Z = 0, AC = 0, P = 0, CY = 0

• A = 0F H, S = 0, Z = 1, AC = 0, P = 0, CY = 0

Infer the usage of Memory Address Register (MAR) in the given scenario where the CPU must read data from a memory location with address 2000 H.

• The CPU places 2000 H into MAR, which is then sent to the address bus

• It holds the data read from memory

• It sets the next program instruction in the PC

• It stores the current stack pointer value

Prioritize the next step in the decode phase where a CPU finished fetching the opcode into the instruction register (IR).

• The control unit interprets the opcode, setting up control signals for the next phase (e.g., ALU operation, memory access)

• It increments the stack pointer by 1

• The CPU discards the opcode

• The CPU discards the Instruction Register

Estimate the status of flag register after execution of the following assembly language program (ALP).
MVI A, 01H ;

DCR A ;

• S=0, Z=1, AC=0, P=1, CY=0

• S=0, Z=1, AC=1, P=0, CY=1

• S=1, Z=1, AC=0, P=0, CY=1

• S=0, Z=0, AC=1, P=1, CY=0

Estimate the status of flag register after execution of the following assembly language program (ALP).

MVI A, FFH

MVI B, 01H

ADD B

• S=0, Z=1, AC=1, P=1, CY=1

• S=1, Z=0, AC=1, P=0, CY=0

• S=1, Z=1, AC=0, P=1, CY=1

• S=0, Z=0, AC=1, P=0, CY=1

Estimate the status of flag register after execution of the following assembly language program (ALP).

MVI A, 40H

MVI B, 10H

SUB B

• S=0, Z=0, AC=0, P=1, CY=0

• S=0, Z=1, AC=1, P=1, CY=0

• S=1, Z=0, AC=1, P=0, CY=1

• S=0, Z=0, AC=1, P=0, CY=1

Estimate the status of flag register after execution of the following assembly language program (ALP).

MVI A, 02H

SUI 05H

• S=1, Z=0, AC=1, P=0, CY=1

• S=0, Z=1, AC=0, P=1, CY=0

• S=1, Z=0, AC=1, P=1, CY=1

• S=0, Z=0, AC=0, P=0, CY=1

Estimate the status of flag register after execution of the following assembly language program (ALP).

MVI A, 50H

CPI 50H

• S=0, Z=1, AC=0, P=1, CY=0

• S=1, Z=0, AC=1, P=1, CY=1

• S=0, Z=0, AC=1, P=0, CY=1

• S=1, Z=1, AC=0, P=0, CY=0