10.1 Assemblers

Question 1

What is an assember?

Answer 1

Translates assembly (abstracted ISA) into machine code

Question 2

What is assembly?

Answer 2

Writing programs specific for an ISA using mnemonics

Question 2

What are mnemonics

Answer 2

• Using short words to describe 1s and 0s operations in the ISA
• A lookup table is used to translate mnemonics to opcodes

Question 3

What is a lexer (and what does it do)

Answer 3

• A lexer turns the source program into a set of tokens.
• A token could be the opcode, operand etc.

Question 4

What is the difference between an assembler and a compiler?

Answer 4

Assembler: Converts assembly to machine code
Compiler: Converts higher level program to machine code

Question 5

What types of convenient notations do assemblers typically allow for

Answer 5

• Labels: Reference next line number
• Named Constants: Can just be replaced with value
• Variables: Can be changed

Question 6

What is the format for Hex 8 assembly

Answer 6

Question 7

How do Labels work in Hex 8 assembly

Answer 7

• Refers to next line

Question 8

How does the hex-8 assembler accomodate for large operands

Answer 8

• Inserts PFIX instructions automatically

Question 9

What does the DATA keyword do in hex-8 assembly?

Answer 9

• Inserts that amount of data into the instruction stream (ie makes room for that many bits in memory)

Question 10

Why does an assember run 2 passes, and what does it do on each pass?

Answer 10

1. Resolve labels and symbols
2. Construct binary

Note: no need to hold entire program in memory

Question 11

What is backpatching

Answer 11

Used to assemble in one pass.
Fixes up labels afterwards.

Downsides: need to store entire program in memory (may be a problem for embedded devices)