From: Baltissen, GJPAA (Ruud) (ruud.baltissen_at_abp.nl)
Date: 2005-10-11 12:05:29
Hallo Gideon, Thank you for your extensive answer! > some are 3.3V. Oops, I indeed completely forgot about that. > ... but the pitfall is the refresh. I realised that as well. The CBM series use some counters to generate the refresh address and are very easy to expand. Regarding the C64, here the VIC-II takes care of the refresh but the problem is that it is impossible to expand. IMHO you're better off building a generator à la CBM. But here comes another problem in view: the CBM refreshes the DRAM with 1 MHz. Good enough for 4164's and 41256's. But AFAIK most DRAM's need a referesh every 1 ms. and that means only 10*10 configurations, read 1M*? DRAM's, can be serviced. Tripling the refresh rate can service 16M*? DRAM's. Am I right? > you need to make a distinction also between an access and a refresh > cycle. It can be done, In the C64 the VIC chip takes care of the refresh. And IMHO it is impossible to detect whether a refresh or an access cycle is going on, please anyone, proof me wrong. And even if possible, that one will be stuck to 1 MHz with the same limitations as described above. Which means I need to build my own generator anyway. But then I have to keep the original DRAM's and the new RAM can only be used outside the original 64 KB. > And then... will you only use 8 bits from the 32-bits that a SIMM > offers? Or do you want to multiplex the data as well? I have a datasheet of a 72 pins 1M*32 module and the pinouts show RAS0..3 and CAS0..3. IMHO this means the data can be accessed 8 bits wise. And the PC is able to perform 8 bits operations, which is difficult with 32 bits only memory. > FPM is slightly different from the 'normal' DRAMs as used in the > C-64. For example, they support auto-refresh modes (cas-before-ras), > but it isnot necessay to use this feature. Secondly, they support > bursting, by asserting cas more often, but once again; you don't > need to use this feature. Why don't I need it? To me it seems it is much simpler to use cas-before-ras because I need less hardware (no generator and extra multiplexers needed). Or do I overlook something? -- ___ / __|__ / / |_/ 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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