From: Baltissen, GJPAA (Ruud) (ruud.baltissen_at_abp.nl)
Date: 2005-10-14 08:16:36
Hallo allemaal, Rather annoying by filling up your email boxes, I'll combine answering Gideons reply with a question I have: I need to switch an input between two outputs, a 1-to-2 demultiplexer. The 74x139 is its 2-to-4 equivalent. Anybody knows such a IC? Hallo Gideon, Remark: this part has to be read with a fixed font. > Using the 8 MHz clock .... I already have a solution (at least I think) and that ones involves the 8 MHz signal as well. I'm going to use two of those delay-IC's, the ones you could find on XT motherboards. For those who don't know what kind of IC this is: this IC has one input and several outputs. The signal presented to the input appears at every output but every time after a certain delay. The dealy for every output varies for every model. The first one is fed by Phi1 and, after some modifying, generates RAS, MUX and CAS needed for a normal read or write access of the DRAMs when Phi2 = (H). The 8 MHz signal is fed to 74LS74 first to generate an out of phase 4 Mhz signal at the /Q output. The Phi1 signal is fed to the CLR input causing the /Q output to remain (H) during Phi2 = (H). If the phase of the 8 MHz signal is not like the figure below, it has to be fed through an invertor first. A shifted flank is not a problem. __ _____ Phi2 : |_______________________| __ __ __ __ __ __ 8 MHZ: |__| |__| |__| |__| |__| _____ _____ ________ 4 MHZ: |_____| |_____| ______ ______ ________ CAS : |____| |____| _______ _______ ________ RAS : |___| |___| The above 4 MHz signal is fed to the second Delay IC and after some modifying a CAS and a RAS are generated, a CAS-before-RAS in this case as you can see. These and the above signals are combined using AND gates and fed to the used DRAMs. -- ___ / __|__ / / |_/ Groetjes, Ruud \ \__|_\ \___| URL: Ruud.C64.org =====DISCLAIMER================================================================= De informatie in dit e-mailbericht is vertrouwelijk en uitsluitend bestemd voor de geadresseerde. Wanneer u dit bericht per abuis ontvangt, verzoeken wij u contact op te nemen met de afzender per kerende e-mail. Verder verzoeken wij u in dat geval dit e-mailbericht te vernietigen en de inhoud ervan aan niemand openbaar te maken. Wij aanvaarden geen aansprakelijkheid voor onjuiste, onvolledige dan wel ontijdige overbrenging van de inhoud van een verzonden e-mailbericht, noch voor daarbij overgebrachte virussen. The information contained in this e-mail is confidential and may be privileged. It may be read, copied and used only by the intended recipient. If you have received it in error, please contact the sender immediately by return e-mail; please delete in this case the e-mail and do not disclose its contents to any person. We don't accept liability for any errors, omissions, delays of receipt or viruses in the contents of this message which arise as a result of e-mail transmission. Message was sent through the cbm-hackers mailing list
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