Chapter 4- Machine Language

Question 1

What is the name of the program that translate assembly code to binary code?

Answer 1

Assembler

Question 2

What are the 3 options to specify and address in assembly code?

Answer 2

1. Direct accessing: express a specific address or use symbol for that address- LOAD R1,67 // R[1] <- 67
2. Indirect addressing: address mode to handle pointers. The instruction specifies memory location that holds the required address

Question 3

Indirect addressing example: x = foo[j];

Write it in assembly

Answer 3

Add R1, foo,j // R1 = foo+j
LOAD R2,R1
STR R2, x

Question 4

What is the hack computer?

Answer 4

16 bit machine builds from CPU, two memory modules- instruction memory and dat memory and two memory mapped i/o devices.
It also has two registers: D and A. They ar 16 bit

Question 5

What is the instruction memory?

Answer 5

It is a read only memory of size 32k 16 bit words

Question 6

What D register is used for?

Answer 6

To store data.

Question 7

What A is used for?

Answer 7

Data register and address register. Means as address In the data memory or address in the instruction memory.
For the instruction memory, jump operations always effect a jump to the instruction located In the memory address by A.
Goto 35, first set A to 35 and then just goto command

Question 8

What is M?

Answer 8

Memory access instructions operate on an implicit memory location labeled M.
M always refers to the memory word who’s address is the current value of A.
D =Memory[516] - 1 so first set A = 516 and then D = M - 1;

Question 9

What is @value

Answer 9

Store value in A. It is the A instruction

Question 10

How many commands to I need when memory location is involved?

Answer 10

Two: one for selecting the address and the second is to operate on the memory location of that address.
Because of that there is the A instruction and the C instruction
To compute

Question 11

What M stands for?

Answer 11

memory[A]

Question 12

What is the format of C instruction?

Answer 12

111a ….

Question 13

How to increment memory[7] and also store it in D?

Answer 13

@7

MD=M+1

Question 14

What is a prequisiof a jump?

Answer 14

That A register holds the value of the instruction line to jump to.

Question 15

If there is a jump we should avoid using

Answer 15

Register M because it can get conflicted with the A register that holds the place to jump.

Question 16

What is the location of the base memory of the screen?

Answer 16

16384. It has 8k rows

Question 17

How is each screen line represented in the computer and from where?

Answer 17

From to left.
Each row has 32 16bit arrays.
Pixel in Row r from the top and column c from the left is:
Mapped to c%16 bit of the array in
RAM[16384 + r*32 + c/16]

Question 18

What is the address of the keyboard and how Does it map?

Answer 18

The address is 24576 and each time a key is pressed, the ASCII of the key appears at memory[24576]

Question 19

What is (symbol)?

Answer 19

It’s a pseudo command that causes the assembler to assign the label symbol to the memory location in which the next command of the program will be stored. It generated NO machine code