1. Assembly Language

2. Computer language hierarchy
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

3. Computer language hierarchy
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)

4. Assembly language
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

5. Programming
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

6. Programming
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.

7. Programming
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

8. Programming
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

9. Assembly programming
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

10. The 8051 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

11. The 8051 instruction set Instruction classes Arithmetic operations
Logical operations
Data transfer
Boolean variable manipulation
Program branching

12. The 8051 instruction set The processor status word (PSW) Carry flag
Auxiliary carry flag
General purpose flags (2)
Register bank selector (2 bits)
Overflow flag
Parity flag

13. The 8051 instruction set Addressing modes Register Direct
Indirect-register
Constant 8-bit
Constant 16-bit
Address 16-bit
Address 11-bit
Relative
Bit

14. Addressing modes
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

15. Data transfer instructions
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 = memory[R0]
MOV R0, A ; R0 = A

16. Simulator 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