From: Gideon Zweijtzer (gideonz_at_dds.nl)
Date: 2005-10-10 20:24:37
Hello Ruud, There are two different kinds of 72-pin SIMM modules; the FPM (Fast page mode) and EDO (Extended Data Out) modules. I would say that the FPM SIMMs are the most compatible with the C-64 hardware. I think that you have to make sure that the 72-pin modules are 5V as well; some are 3.3V. 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 is not 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. The biggest difference is the geometry. The C-64 rams use an 8x8 address bit matrix (resulting in 2^8 * 2^8 addresses per chip (65536 addresses); 1 bit per chip, 8 chips => 64kB). The 72-pin SIMMs have different geometries, such as 9*9, 8*10, 9*10, etc.. I think it would not be hard to multiplex those from the bank register that you need for bank switching anyway, but the pitfall is the refresh. Since the VIC chip generates the refresh cycles by actually counting through the rows, only 2^8 of all rows will be refreshed on the SIMM. In addition to the multiplexing of the additional row/column bits, you need to make a distinction also between an access and a refresh cycle. It can be done, but it requires some logic. I think it can be done by using a counter that counts the 8 MHz clock (synchronized by the PHI2), and switching the mux according to the output of this three-bit counter. 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? Gideon > > Hallo allemaal, > > > Has anybody experience with using a 72 pins DRAM module in > combination with the C64? I need RAM but much much more than > the 256 KB I get when replacing the original 4164s with 41256s. > > Thanks for any input! > > > -- > ___ > / __|__ > / / |_/ 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 > Message was sent through the cbm-hackers mailing list
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