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This module will provide a brief introduction into Assembly Language.

Assembly language

Assembly language , commonly referred to as assembly, is a more human readable form of machine language. Every computer architecture uses its own assembly language. So processors using an architecture based on the x86, PowerPC, or TI DSP will each use their own language. Machine language is the pattern of bits encoding a processor's operations. Assembly will replace those raw bits with a more readable symbols call mnemonics .

For example, the following code is a single operation in machine language. 0001110010000110 For practical reasons, a programmer would rather use the equivalent assembly representation for the previous operation. ADD R6,R2,R6 ; Add $R2 to $R6 This is a typical line of assembly. The op code ADD instructs the processor to add the operands R2 and R6 , which are the contents of register R2 to register R6, and store the results in register R6. The " ; " indicates that everything after that point is a comment, and is not used by the system.

Assembly has a one-to-one mapping to machine language. Therefore, each line of assembly corresponds to an operation that can be completed by the processor. This is not the case with high-level languages. The assembler is responsible for the translation from assembly to machine language. The reverse operation is completed by the dissasembler .

Assembly instructions are very simple, unlike high-level languages. Often they only accomplish a single operation. Functions that are more complex must be built up out of smaller ones.

The following are common types of instructions:

  • Moves:
    • Set a register to a fixed constant value
    • Move data from a memory location to a register (a load) or move data from a register to a memory location (a store). All data must be fetched from memory before a computation may be performed. Similarly, results must be stored in memory after results have been calculated.
    • Read and write data from hardware devices and peripherals
  • Computation:
    • Add, subtract, multiply, or divide. Typically, the values of two registers are used as parameters and results are placed in a register
    • Perform bitwise operations, taking the conjunction/disjunction (and/or) of corresponding bits in a pair of registers, or the negation (not) of each bit in a register
    • Compare two values in registers (>,<,>=, or<=)
  • Control Flow:
    • Jump to another location in the program and execute instructions there
    • Jump (branch) to another location if a certain condition holds
    • Jump to another location, but save the location of the next instruction as a point to return to (a call)

Advantages of assembly

The greatest advantage of assembly programming is raw speed. A diligent programmer should be able to optimize a piece of code to the minimum number of operations required. Less waste will be produced by extraneous instructions. However, in most cases, it takes an in-depth knowledge of the processor's instruction set in order to produce better code than the compiler writer does. Compilers are written in order to optimized your code as much as possible, and in general, it is hard to write more efficient code than it.

Low-level programming is simply easier to do with assembly. Some system-dependent tasks performed by operating systems simply cannot be expressed in high-level languages. Assembly is often used in writing device drivers , the low level code that is responsible for the interaction between the operating system and the hardware.

Processors in the embedded space, such as TI's MSP430 , have the potential for the greatest gain in using assembly. These systems have very limited computational resources and assembly allows the maximum functionality from these processors. However, as technology is advancing, even the lowest power microcontroller is able to become more powerful for the same low cost.

Questions & Answers

what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
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are you nano engineer ?
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fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
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That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
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Mostly, they use nano carbon for electronics and for materials to be strengthened.
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is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
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Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
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Do you know which machine is used to that process?
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for screen printed electrodes ?
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of graphene you mean?
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or in general
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in general
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Graphene has a hexagonal structure
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Source:  OpenStax, Microcontroller and embedded systems laboratory. OpenStax CNX. Feb 11, 2006 Download for free at http://cnx.org/content/col10215/1.29
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