In many cases we work with more than four components

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Unformatted text preview: hy of abstraction at the hardware level might be: 1. transistors; 2. logic gates, memory cells, special circuits; 3. single-bit adders, multiplexers, decoders, flip-flops; 4. word-wide adders, multiplexers, decoders, registers, buses; 5. ALUs (Arithmetic-Logic Units), barrel shifters, register banks, memory blocks; 6. processor, cache and memory management organizations; 7. processors, peripheral cells, cache memories, memory management units; 8. integrated system chips; 9. printed circuit boards; 10. mobile telephones, PCs, engine controllers. The process of understanding a design in terms of levels of abstraction is reasonably concrete when the design is expressed in hardware. But the process doesn't stop with the hardware; if anything, it is even more fundamental to the understanding of software and we will return to look at abstraction in software design in due course. Gate-level design The next step up from the logic gate is to assemble a library of useful functions each composed of several gates. Typical functions are, as listed above, adders, multiplexers, decoders and flip-flops, each 1-bit wide. This book is not intended to be a gen- MU0 - a simple processor 7 eral introduction to logic design since its principal subject material relates to the design and use of processor cores and any reader who is considering applying this information should already be familiar with conventional logic design. For those who are not so familiar with logic design or who need their knowledge refreshing, 'Appendix: Computer Logic' on page 399 describes the essentials which will be assumed in the next section. It includes brief details on: Boolean algebra and notation; binary numbers; binary addition; multiplexers; clocks; sequential circuits; latches and flip-flops; registers. If any of these terms is unfamiliar, a brief look at the appendix may yield sufficient information for what follows. Note that although the appendix describes these circuit functions in terms of simple logic gates, there are often more efficient...
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