IT training ARM assembly language programming cockerell 1987 07
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IT training ARM assembly language programming cockerell 1987 07
Title PageARMAssembly Language ProgrammingBy Pete CockerellComputer Concepts Ltd • Gaddesden Place Hemel Hempstead • Hertfordshire HP2 6EX • ENGLAND1 IT training ARM assembly language programming cockerell 1987 07 of 1ARM Assembly Language Programming - Chapter 1 - Firs1. First ConceptsLike most interesting subjects, assembly language programming requires a little background knowledge before you can start to appreciate it. In this chapter, we explore these basics. If terms such as two's complement, hexadecim IT training ARM assembly language programming cockerell 1987 07al, index register and byte are familiar to you. the chances are you can skip to the next chapter, or skim through this one for revision. Otherwise, mIT training ARM assembly language programming cockerell 1987 07
ost of the important concepts you will need to understand to start programming in assembler are explained below.One prerequisite, even for the assemblTitle PageARMAssembly Language ProgrammingBy Pete CockerellComputer Concepts Ltd • Gaddesden Place Hemel Hempstead • Hertfordshire HP2 6EX • ENGLAND1 IT training ARM assembly language programming cockerell 1987 07parisons to similar ideas in BASIC, c or Pascal. If you don't have this fundamental requirement, you may as well stop reading now and have a bash at BASIC first.1.1 Machine code and up...The first question we need to answer is. of course. 'What is assembly language'. As you know, any programming lan IT training ARM assembly language programming cockerell 1987 07guage is a medium through which humans may give instructions to a computer. Languages such as BASIC. Pascal and c. which we call high-level languages,IT training ARM assembly language programming cockerell 1987 07
bear some relationship to English, and this enables humans to represent ideas in a fairly natural way. For example, the idea of performing an operatiTitle PageARMAssembly Language ProgrammingBy Pete CockerellComputer Concepts Ltd • Gaddesden Place Hemel Hempstead • Hertfordshire HP2 6EX • ENGLAND1 IT training ARM assembly language programming cockerell 1987 07to write programs in a relatively painless way, they in fact bear little relationship to the way in which the computer performs the operations. All a computer can do is manipulate patterns of'on' and 'off, which are usually represented by the presence or absence of an electrical signal.To explain th IT training ARM assembly language programming cockerell 1987 07is seemingly unbridgable gap between electrical signals and our familiar FOR.. .NEXT loops, we use several levels of representation. At the lowest levIT training ARM assembly language programming cockerell 1987 07
el we have our electrical signals. In a digital computer of the type we're interested in. a circuit may be at one of two levels, say 0 volts ('oft') oTitle PageARMAssembly Language ProgrammingBy Pete CockerellComputer Concepts Ltd • Gaddesden Place Hemel Hempstead • Hertfordshire HP2 6EX • ENGLAND1 IT training ARM assembly language programming cockerell 1987 07some visual representation. The digits 0 and 1 are used. These digits are used because, in addition to neatly representing the idea of an absence or presence of a signal, 0 and 1 are the digits of the binary number system, which is central to the understanding of how a computer works. The term binar IT training ARM assembly language programming cockerell 1987 07y digit is usually abbreviated to bit. Here is a bit: 1. Here are eight bits in a row: 110110111 of 20.................................... _ARM AssemIT training ARM assembly language programming cockerell 1987 07
bly Language Programming - Chapter 1 - FirsMachine codeSuppose we have some way of storing groups of binary digits and feeding them into the computer.Title PageARMAssembly Language ProgrammingBy Pete CockerellComputer Concepts Ltd • Gaddesden Place Hemel Hempstead • Hertfordshire HP2 6EX • ENGLAND1 IT training ARM assembly language programming cockerell 1987 07 that pattern its response will be the same. Let's say we have a mythical computer which reads in groups of bits eight at a time, and according to the pattern of Is and Os in the group, performs some task. On reading this pattern, for example10100111the computer might produce a voltage on a wire, an IT training ARM assembly language programming cockerell 1987 07d on reading the pattern10100110it might switch off that voltage. The two patterns may then be regarded as instructions to the computer, the first meaIT training ARM assembly language programming cockerell 1987 07
ning 'voltage on', the second 'voltage off. Every time the instruction 10100111 is read, the voltage will come on, and whenever the pattern 10100110 iTitle PageARMAssembly Language ProgrammingBy Pete CockerellComputer Concepts Ltd • Gaddesden Place Hemel Hempstead • Hertfordshire HP2 6EX • ENGLAND1 IT training ARM assembly language programming cockerell 1987 07achinery reacts to.Assembly language and assemblersThere are 256 combinations of eight Is and 0s. from 00000000 to 11111111. with 254 others in between. Remembering what each of these means is asking loo much of a human: we are only good at remembering groups of at most six or seven items. To make t IT training ARM assembly language programming cockerell 1987 07he task of remembering the instructions a little easier, we resort to the next step in the progression towards the high-level instructions found in BAIT training ARM assembly language programming cockerell 1987 07
SIC. Each machine code instruction is given a name, or mnemonic- Mnemonics often consist of three letters, but this is by no means obligatory. We coulTitle PageARMAssembly Language ProgrammingBy Pete CockerellComputer Concepts Ltd • Gaddesden Place Hemel Hempstead • Hertfordshire HP2 6EX • ENGLAND1 IT training ARM assembly language programming cockerell 1987 07ON is easier to remember. A program written using these textual names for instructions is called an assembly language program, and the set of mnemonics that is used to represent a computer's machine code is called the assembly language of that computer. Assembly language is the lowest level used by IT training ARM assembly language programming cockerell 1987 07humans to program a computer: only an incurable masochist would program using pure machine code.It is usual for machine codes to come in groups whichIT training ARM assembly language programming cockerell 1987 07
perform similar functions. For2 of 20........................ ~_ ARM Assembly Language Programming - Chapter 1 - Firsexample, whereas 10100111 might mTitle PageARMAssembly Language ProgrammingBy Pete CockerellComputer Concepts Ltd • Gaddesden Place Hemel Hempstead • Hertfordshire HP2 6EX • ENGLAND1 IT training ARM assembly language programming cockerell 1987 07structions are 'on' ones, but they affect different signals. Now we could define two mnemonics, say ONO and ONI. but it is much more usual in assembly language to use the simple mnemonic ON and follow this with extra information saying which signal we want to switch on. For example, the assembly lan IT training ARM assembly language programming cockerell 1987 07guage instructionON 1would be translated into 10101111. whereas:Title PageARMAssembly Language ProgrammingBy Pete CockerellComputer Concepts Ltd • Gaddesden Place Hemel Hempstead • Hertfordshire HP2 6EX • ENGLAND1 Title PageARMAssembly Language ProgrammingBy Pete CockerellComputer Concepts Ltd • Gaddesden Place Hemel Hempstead • Hertfordshire HP2 6EX • ENGLAND1Gọi ngay
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