• High Level Language
• Assembly language
• Machine language
• Compiled or interpreted
• One statement maps to one or more assembly language statement
• Assembled
• One statement maps to one machine language instruction
• Loaded directly into the processor memory
• One statement maps to one or more RTL statements

• You can toss in the scripting languages
(PERL, Python, PHP, VBScript…)
• You can toss in the interpreted languages
(BASIC, Haskell, Lisp, Forth)
• And other categories
• The seem to fit somewhere between HLL and
Assembly but don’t run directly on the hardware (virtual machine/interpreter)

• This is as close as you ever get to the hardware (without actually keying in binary values – which no one ever does anymore)
• Requires a major shift in mindset from programming HLLs

• In HLL programming you concern yourself with variables, datatypes, and control statements
– int, float, char, if, for, while, arrays, etc.
• In assembly language programming you concern yourself with memory and instruction
– RAM, ROM, registers, instruction classes, addressing modes

• In HLL programming you concern yourself with keywords and grammars
– Statements, expressions, etc.
• In assembly language programming you concern yourself with mnemonics and circuit components
– Instruction names, arithmetic units, control units, etc.

• In HLL programming you sit down with a
“how to” textbook to guide you
• In assembly language programming you sit down with a chip specification document to guide you

• In HLL programming you might be able to estimate how long a program will take to run and how much memory it will use
• In assembly language programming you can calculate how long a program will take to run and how much memory it will use

• You must have an understanding of the architecture on which you are running your program
• Each architecture [or family] has it’s own assembly language
– The language is intimately tied to the design of the architecture

• 8-bit CPU with A (accumulator) and B registers
• 16-bit program counter and data pointer
• 8-bit program status word
• 8-bit stack pointer
• Internal ROM
• Internal RAM
– Four register banks of 8 registers each
– Sixteen bytes of bit addressable locations
– Eighty bytes of general purpose data memory
– Thirty two input/output pins
• Two 16-bit timer/counters
• Various control registers
• Serial port
• Interrupt sources

• Instruction classes
– Arithmetic operations
– Logical operations
– Data transfer
– Boolean variable manipulation
– Program branching

• The processor status word (PSW)
– Carry flag
– Auxiliary carry flag
– General purpose flags (2)
– Register bank selector (2 bits)
– Overflow flag
– Parity flag

• Addressing modes
– Register
– Direct
– Indirect-register
– Constant 8-bit
– Constant 16-bit
– Address 16-bit
– Address 11-bit
– Relative
– Bit

• Rn where 0 ≤ n ≤ 7 – the contents of register n;
• 0x00 (or other hex number) – the contents of a memory location
• @Ri where 0 ≤ i ≤ 1 – indirect, register holds the memory address
• #0x00 (or other hex number) – 8-bit constant number
• #0x00 16 (or other hex number) – 16-bit constant number
• There are a few others but these are the most commonly used modes

• MOV op-code
• Various operands dependant on desired addressing mode
– Some examples:
MOV A, R0 ; A = R0
MOV A, #0x00 ; A = 0
MOV A, 0x00 ; A = memory[0]
MOV A, @R0 ; A = memory[R0]
MOV R0, A ; R0 = A

• We don’t have an 8051 processor
• The next best thing is a simulator
• Download EdSim51 from EdSim51
– This is a Java executable (.jar) file that runs on both Windows and MacOS
• Documentation is available on the download site