1. Assembly Language
part 1

2. Some terminology
Assembly language: a low-level language that is a little more human-friendly than machine language
assembler: a program that translates assembly language source code into executable form
object code: machine language program (assembler output)

3. Types of assemblers
Resident assembler: an assembler written for its own platform, using the native instruction set
Cross assembler: assemble run on one platform to produce object code for another
Disassembler: program that attempts to recover source code from object code (not 100% successful)

4. Assembly language instructions
Mnemonics: abbreviated words used instead of machine language hex code;
have one-to-one correspondence with underlying instruction
always possible to determine underlying machine language statement from assembly language mnemonic, but not vice-versa
Pseudo-ops: assembly language statements used mostly for data declaration; do not correspond to specific machine language instructions

5. Pep/8 assembly language
General syntax notes:
one instruction per line of code
comments start with semicolon, continue until end of line
not case-sensitive
Spacing:
at least one space required after each instruction (mnemonic or pseudo-op)
otherwise doesn’t matter
last line of program must be .END pseudo-op

6. Pep/8 Assembly Language
Mnemonic instruction format:
2-6 letter instruction specifier (most or 3-4 letters)
operand specifier, usually followed by a comma and
1-3 letter address mode specifier (most are 1)
Examples:
LDA 0x0014,i ; load hex value 14 to A
LDX 0x1110,d ; load data at address 1110 into x
Entire Pep/8 assembly language instruction set is printed on the inside front cover (and on page 191) of your textbook

7. Pep/8 Assembly Language
Addressing mode specifiers:
i: immediate
d: direct
n: indirect
s: stack-relative
sf: stack-relative deferred
x: indexed
sx: stack-indexed
sxf: stack-indexed deferred

8. Pep/8 Assembly Language
Unimplemented opcodes
instructions available at assembly language level, even though they are not (directly) available at the machine language level
represent operations handled by the operating system
They include:
NOPn: unary no operation trap
NOP: non-unary NOP
DECI: decimal input trap
DECO: decimal output trap
STRO: string output trap

9. Pseudo-ops .ADDRSS: used to crate labeled jump destinations
.ASCII: specifies char string
.BLOCK: allocates specified # of bytes, initializes whole set to zero
.BURN: used for OS configuration
.BYTE: allocates one byte; can specify hex or decimal content
.END: stop code
.EQUATE: equate symbol with literal value; like # define in C/C++
.WORD: allocates one word of memory

10. Example program 1 ; Program example 1 CHARO 0x0010 ,d CHARO 0x0011 ,d
STOP
.ASCII "Arrr!"
.END
Comment
Instructions: each outputs one
character; starting address of program
is 0000, and each instruction (except
STOP) is 3 bytes long; STOP is one
byte
Data

11. Object code & assembler output from program example 1