Microprocessors - Question and Answer - 6

26. What happens when HLT instruction is executed in processor ?
The Micro Processor enters into Halt-State and the buses are tri-stated. In the x86 computer architecture, HLT (halt) is an assembly language instruction which halts the central processing unit (CPU) until the next external interrupt is fired. The HLT instruction is executed by the operating system when there is no immediate work to be done, and the system enters its idle state.

27. What are the three types of buses ?
Address bus: This is used to carry the Address to the memory to fetch either Instruction or Data.
Data bus : This is used to carry the Data from the memory.
Control bus : This is used to carry the Control signals like RD/WR, Select etc.

28. What does EU do ?
Execution Unit receives program instruction codes and data from BIU, executes these instructions and store the result in general registers.Execution unit. In computer engineering, an execution unit (also called a functional unit) is a part of the central processing unit (CPU) that performs the operations and calculations as instructed by the computer program.

29. Which Stack is used in 8086 ?  
FIFO (First In First Out) stack is used in 8086.In this type of Stack the first stored information is retrieved first. In 8086, the main stack register is called stack pointer - SP. The stack segment register (SS) is usually used to store information about the memory segment that stores the call stack of currently executed program.

30. What is the RST for the TRAP ?
RST 4.5 is called as TRAP. INTR, RST 7.5, RST 6.5, RST 5.5 are maskable interrupts in 8085 microprocessor. TRAP is a non-maskable interrupt. It consists of both level as well as edge triggering and is used in critical power failure conditions.