Chapter 14 - Assembly Language

Question 1

What is a mnemonic

Answer 1

A mnemonic is a letter representation of machine code

Question 2

What is a numeric code?
Describe 1xx

Answer 2

A numeric code consists of 3 characters. ADD’s numeric code is 1xx. The first character is an OP code (which defines the function of mnemonic) and the xx is the operand which describes the memory address/value the OP code functions upon.

Question 3

Instruction: Add

Answer 3

Mnemonic: ADD
Numeric code: 1xx
Adds the contents of the memory address to the accumulator

Question 4

Instruction: Subtract

Answer 4

Mnemonic: SUB
Numeric code: 2xx
Subtracts the contents of the memory address from the accumulator

Question 5

Instruction: Store

Answer 5

Mnemonic: STA
Numeric code: 3xx
Stores the value in the accumulator in the memory address given

Question 6

Instruction: Load

Answer 6

Mnemonic: LDA
Numeric code: 5xx
Load the accumulator with the contents of the memory address given.

Question 7

Instruction: Branch (always) (uncondictional)

Answer 7

Mnemonic: BRA
Numeric code: 6xx
Branch - always uses the address given as the address of the next instruction (by changing PC).

Question 8

Instruction: Branch if zero

Answer 8

Mnemonic: BRZ
Numeric code: 7xx
Branch to the address given if the accumulator is zero

Question 9

Instruction: Branch If Positive

Answer 9

Mnemonic: BRP
Numeric code: 8xx
Branch to the address given if the accumulator is zero or positive

Question 10

Instruction: Input

Answer 10

Mnemonic: INP
Numeric code: 901
Input into the accumulator

Question 11

Instruction: Output

Answer 11

Mnemonic: OUT
Numeric code: 902
Output contents of the accumulator

Question 12

Instruction: Halt

Answer 12

Mnemonic: HLT
Numeric code: 0
Stops the execution of the program

Question 13

Instruction: Data

Answer 13

Mnemonic: DAT
Numeric code: n/a
Used to indicate a location that contains data.

Question 14

Which LMC instructions allow you to change the Program Counter (PC)

Answer 14

Branch (unconditional) - BRA, Branch if zero (conditional) - BRZ, Branch if positive (conditional) - BRP.

Question 15

Addressing mode (overview)

Answer 15

The last 2 digits within the operation code (OP code)

Question 16

Addressing mode (detail)

Answer 16

intermediate addressing: the operand is the actual value upon which the instruction is to be performed upon

direct addressing: the operand holds the memory address location of the value to be operated upon (only mode available in LMC)

indirect addressing: the operand is the location (typically a register) which holds the address we want - a larger range of accessible locations

indexed addressing: the address of the operand is obtained by adding the contents of a general register (index register) to a constant value. Included in istruction code and used to access arrays with successive order