(1) Question: Describe different types of instruction.
Answer:
Instructions available in a processor may be broadly classified into six
groups.
This are(i)
Data transfer instructions
(ii) Arithmetic instructions
(iii) Logical instructions
(iv) Program control instructions
(v) System control instructions
(vi) I/O instructions
(i) Data transfer instructions: Data transfer instructions are concerned
primarily with data transfers between the processor and main memory.
Typically an ideal instruction set must be able to handle the following
transfers:
Register to register
Register to memory
Memory to register
Memory to memory
(ii) Arithmetic instructions: All instruction sets typically include ADD
and SUBTRACT instructions.
Example: LEA Z, A2; Load the address of Z into the address register
A2.
(iii) Logical instructions: Invariably, the instruction sets of all
contemporary processors include instructions to perform Boolean AND,
OR, NOT and EXCLUSIVE-OR operations on a bit-by-bit basis.
Page 4 of 63
Example: LSR.W #3,D5 – This instruction performs a left logical shift
of the low-order, 16 bits of the data register D5 by three places.
(iv) Program control instructions: In a conventional computer,
instructions are always executed in the same order they are presented.
Instructions that perform this are called program control instructions.
These instructions may be classified into four groups:
· Unconditional branch instructions
Conditional branch instructions
Subroutine call instructions
Interrupt handling instructions
Example: MOV AB X, R7; Move the address of X register into R7.
(v) System control instructions: With the advent of low cost VLSI
microprocessors, designing systems with several processors is feasible.
Such a multiprocessor system has significant advantage, such as high
processing speed and more reliability.
Example: LOOP1 TAS TEST
BNE LOOP1
CLR.B TEST
(vi) I/O instructions: I/O instructions allow a processor to perform input
and output operations. An input instruction allows a peripheral to
transfer a word to either a CPU register to memory. Similarly, an output
instruction enables a processor to transfer a word into the buffer register
of a peripheral device.
Example: IN, OUT.