addressing modes

Question 1

opcode consists of

Answer 1

binary digits representing basic operation eg ADD/LOAD and 2 digit code/bit pattern representing addressing mode

Question 2

immediate addressing

Answer 2

operand is the actual value to be operated on (eg LDA #5)

Question 3

direct addressing

Answer 3

operand holds the memory address of the value to be operated on, data hardcoded into instruction (only addressing mode used in LMC assembly language) (eg LDA 5)

Question 4

indirect addressing

Answer 4

operand is the location (typically register) which holds address of data we want. (eg LDA (5)) starting address stored in block of memory ie index table

Question 5

uses of indirect addressing

Answer 5

Enables a larger range of addressable locations and allows calling routine whose starting point may move eg if x = 1009. store 1009 at 4000 and go via BRA 4000. if routine moves from 1009, only change contents of 4000

Question 6

indexed addressing

Answer 6

address of the operand is obtained by adding a constant value/address to the contents of a general register aka INDEX REGISTER. constant val and the number of the index register are in the instruction code

Question 7

index addressing use

Answer 7

to access an array whose elements in successive memory locations
useful for a table of routine start addresses

Question 8

immediate addressing adv and uses

Answer 8

• uses no memory, so fastest

- used when using a constant rather than variable

Question 9

direct addressing adv, disadv and uses

Answer 9

-fast (not as fast as immediate)
BUT -code depends on correct data always being present
uses: computers only running single program eg engine management computer so good for quick access too

Question 10

indirect addressing uses

Answer 10

if loader loads software libraries in different memory location each time when program is loaded