Data Transfer Instruction

What is the data transfer instruction? Give example.

Data transfer instructions move data between registers or between memory and registers. For example:

• String Forms:

movsb ;move string byte by byte

movsw ;move string word by word

EXAMPLE:

Movsb es, ds ;Copies 8 bits at DS:SI to ES:DI

• New String Form (386+):

movzx ;move string with zero extended

movsx ;move string with sign extended

EXAMPLE:

movsx cx, al ;cl get al

movzx cx,al ;cl gets al

polling in 8085 microprocessor

What do you mean by polling in 8085.

When the microprocessor receives an Interrupt Service Request (ISR) on the interrupt line it must determine which of the devices connected to that input sent the request.

Software Polling is one method by which it can do so.

In Software Polling:

A software routine is used to identify the device requesting service. It does so by checking each device to see if it was the one needing service.

hardware interrupts in 8085 microprocessor

Explain hardware interrupts in 8085.

• When a device interrupts, it actually wants the MP to give a service which is equivalent to asking the MP to call a subroutine. This subroutine is called ISR (Interrupt Service Routine)
• Interrupts:
• The 8085 microprocessor has 5 interrupts. They are presented below in the order of their priority (from lowest to highest):
• INTR is mask able 8080Acompatible interrupt. When the interrupt occurs the processor fetches from the bus one instruction.
• RST5.5 is a mask able interrupt. When this interrupt is received the processor saves the contents of the PC register into stack and branches to 2Ch (hexadecimal) address.
• RST6.5 is a mask able interrupt. When this interrupt is received the processor saves the contents of the PC register into stack and branches to 34Ch (hexadecimal) address.
• RST7.5 is a mask able interrupt. When this interrupt is received the processor saves the contents of the PC register into stack and branches to 3Ch (hexadecimal) address.
• Trap is a non-maskable interrupt. When this interrupt is received the processor saves the contents of the PC register into stack and branches to 24h (hexadecimal) address.
• All maskable interrupts can be enabled or disabled using EI and DI instructions. RST 5.5, RST6.5 and RST7.5 interrupts can be enabled or disabled individually using SIM instruction.

Processor Cycle

What is meant by processor cycle?

Processor Cycle is a term used to describe one aspect of a processor's performance: the number of clock cycles that happen when an instruction is being executed.

SIM Instruction in 8085 microprocessor

What is the function performed by SIM Instruction?

The SIM instruction in the 8085 microprocessor is used to set (SIM) the interrupt mask. With SIM, you can mask or unmask RST5.5, RST6.5, and RST7.5, you can reset the pending RST7.5 flip flop, and you can set or reset the SOD (Serial Output Data) pin.

difference between hardware and software interrupts in 8085 microprocessor

Differentiate between hardware interrupts and software interrupts of 8085.

• The software interrupt is initiated by the main program, but the hardware interrupt is initiated by an external device.
• In 8085, the software interrupt cannot be disabled or masked but the hardware interrupt except TRAP can be disabled or masked.

CMA instruction in 8085

Explain the execution of the instruction CMA in 8085.

CMA - Complement Accumulator

The Complement Accumulator (CMA) instruction provides a 1’s complement of the 8 bits in the A register, i.e the 1’s are set to 0’s and the 0’s are set to 1’s.