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Questions and Answers of 8085 Microprocessor (Part-I)

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What is a microprocessor?
A microprocessor is a multipurpose, programmable, clock driven register and ALU based electronic device. It reads binary instructions from memory, accepts binary data as input, processes data and provides result as output.

What are the various registers in 8085?
8085 has 8-bit accumulator (A), six 8-bit general purpose registers B, C, D, E, H and L, temporary data register, W and Z registers, flag register, instruction register, 16-bit program counter (PC) and 16-bit stack pointer (SP).

What are the various flags in a flag register?
Flag register is an 8-bit register in which five of the bits carry significant information in form of flags. They are S (Sign flag), Z (Zero flag), AC (Auxiliary Carry flag), P (Parity flag) and CY (Carry flag).

What is the function of accumulator?
Accumulator is an 8-bit register which is used in arithmetic, logic, load, store and input/output operations. It is also used to store the result of arithmetic and logical operations.

What is the function of program counter?
The program counter (PC) is a 16-bit special purpose register which, at a given time, stores the address of the next instruction to be fetched. It acts as a pointer to the next instruction.

What is the function of instruction register?
The processor first fetches the opcode of the instruction from the memory and stores the opcode in instruction register. This opcode is then sent to the instruction decoder to decode it.

What are hardware interrupts in 8085?
There are five hardware interrupts in 8085. They are TRAP, RST 7.5, RST 6.5, RST 5.5, INTR.

What are addressing modes in 8085?
The different methods used to select or address the operands are called addressing modes. There are five addressing modes in 8085. They are register addressing mode, immediate addressing mode, direct addressing mode, indirect addressing mode and implied addressing mode.

What happens when HLT instruction is executed?
When HLT instruction is executed, the microprocessor enters into halt state and the buses are tristated.

What is a bus?
A bus is a group of parallel conducting lines that carries data, address and control signals. The various units in microprocessor are connected by the three sets of parallel lines called buses. The three buses are the address bus, the data bus and the control bus.
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