Download Some “facts” about software…

Assembly Language
Computer language hierarchy
• High Level Language
• Compiled or interpreted
• One statement maps to one
or more assembly language
statement
• Assembly language
• Assembled
• One statement maps to one
machine language
instruction
• Machine language
• Loaded directly into the
processor memory
• One statement maps to one
or more RTL statements
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)
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
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
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.
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
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
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
The 8051 architecture
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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
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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
The 8051 instruction set
• Instruction classes
– Arithmetic operations
– Logical operations
– Data transfer
– Boolean variable manipulation
– Program branching
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
The 8051 instruction set
• Addressing modes
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Register
Direct
Indirect-register
Constant 8-bit
Constant 16-bit
Address 16-bit
Address 11-bit
Relative
Bit
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
Data transfer instructions
• MOV op-code
• Various operands dependant on desired
addressing mode
– Some examples:
MOV
MOV
MOV
MOV
MOV
A, R0
A, #0x00
A, 0x00
A, @R0
R0, A
;
;
;
;
;
A = R0
A = 0
A = memory[0]
A = memory[R0]
R0 = A
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