DatapathComponents0 - Datapath Components Introduction Have...

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Datapath Components Introduction Have determined that can decompose system into Datapath and control Identified Datapath as Route(s) data takes through system Components through which data passes As it moves through system Control elements Mechanisms or means for orchestrating /managing flow along datapath Observed that datapath components comprise myriad of collection of Analog, digital, mechanical, etc. pieces Key point with each Each encapsulates a specific high-level function Piece of functionality Each contributes that functionality To support intended function of the design Want to now briefly touch on some of more common digital ones Earlier identified number of common operations or functions to be performed Store Transfer Select Direct or route Modify Arithmetic Logical Encode / decode Let’s examine components that affect those operations Selection – Multiplexing In context of datapath Selection entails choosing data from any of number of different sources - 1 of 51 -
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Potential sources include Memory Supporting or companion processor PLD Port Potential targets include same set From abstract perspective Selection is simply multiplexing in time Following diagram presents high-level model of Selection function The illustrated module Inputs n data sets with m signals each log 2 n selector lines Output enable control Outputs One data set with m signals Selected from the n input sets Simple selector / multiplexer Choosing between two alternate data sets Given in accompanying figure The enable control may or may not be included Design can be extended Increasing Number of inputs Corresponding number of selector lines In Verilog at can be modeled at Data flow or behavioural level as If-else construct Switch or case statement Gate level as Collection of tristate gates Combination of AND and OR gates - 2 of 51 -
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