List four interrupts of 8085 microprocessor

List four interrupts of 8085.

INTERRUPTS OF 8085

• INTR,
• RST7.5
• RST6.5
• RST5.5

similarities between CALL_RET and PUSH_POP instructions

List out the similarities between CALL_RET and PUSH_POP instructions.

When CALL is executed the microprocessor automatically stores the 16-bit address of the instruction next to CALL on the stack pointer.

The programmer uses the instruction PUSH to save the contents of the register pair on the stack.

RET transfers the contents of the top two locations of the stack to the PC.	POP transfers the contents of the top two locations of the stack to the specified register pair.
Has 8 conditional RETURN instructions.	No conditional POP instructions.

initiate hardware interrupts in 8085 microprocessor

List the type of signals that have to be applied to initiate hardware interrupts in 8085.

It has three pins for interrupts; NMI, IRQ and FIRQ. A low level on any of these pins will cause an interrupt. The machine state will then be stacked and the routine entered. The appropriate routine address is found in a table of interrupt vectors. Two locations are dedicated to each Interrupt pin, in which are loaded the two bytes of the interrupt routine address.

An order of priority is imposed - the interrupts at the top of the list set the flag bits of the other interrupts to stop them interrupting during the interrupt service routine. The former values of these bits are restored when the flag register is pulled off the stack on return from the interrupt. Further interrupts are then free to occur thereafter.

instruction format of 8085 microprocessor

What is the instruction format of 8085.

The instruction set is grouped into the following formats:

	Task Op		code
1 BYTE	Copy the contents of the accumulator in the register C.		MOV C,A
2 BYTE	Load an 8-bit data byte in the accumulator		MVI A,data
3 BYTE		Transfer the program sequence to the memory location 2085H.	JMP 2085H

machine cycles of 8085 microprocessor

List the various machine cycles of 8085.

Each time the CPU executes an instruction, it takes a series of steps. The complete series of steps is called a machine cycle. A machine cycle can be divided into two smaller cycles. These are instruction cycle and execution cycle.

7 MACHINE CYCLES

Opcode fetch

Memory read

Memory write

I/O read

I/O write

interrupt acknowledge

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