What is the goal of the ALU control? To 1) conserve power or 2) to insure that the ALU gives up the answer within a fixed time? As Olin has pointed out, the power issue is probably not really much of an issue (depending, of course, upon the technology used to implement the ALU and the entire CPU. As for point #2, you are most likely building a synchronous system, in which case there are a lot more to it then simply controlling the coming and goings of the ALU; otherwise you're building an asynchronous systems, in which case the ALU ON/OFF control is the least of your worries. If you're controlling the ALU simply because you don't like the idea of "messy" outputs from the ALU due to "messy" inputs TO the ALU, you probably are building much of a CPU. There's a lot more to CPU design than the ALU. Douglas Wood Software Engineer dbwood@kc.rr.com ICQ#: 143841506 Home of the EPICIS Development System for the PIC http://epicis.piclist.com ----- Original Message ----- From: "Peter L. Peres" To: Sent: Thursday, June 26, 2003 12:05 AM Subject: Re: [EE]: ALU Enable > >Why? Can't the ALU do anything it wants, as long as you ignore its > >outputs? If you're using old TTL (Is there an HC181?), the power > >dissipation won't change much anyway... > > Depending on how glitchy whatever is at the inputs, the outputs may not > settle in time under certain conditions. This is why a synchronous > pipeline is probably the best way to do it. > > Peter > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads