Hallo Patryk, > Could be used as a test / starting point but extra bits > would have to be added. IMHO you haven't understood me. By demirroring the VIC and SID you have created the room to add those extra bits. A part can be used to add extra I/O, for example a 6526 that gives you the bits to select the wanted Kernal, other parts give you room for RAM and ROM. To be honest, this idea is not mine, has been published in a 64er. But the 64er did the demirroring on the board, something you don't want to do. Now use the technique (partly) used on the 6502-RAMROM. First you have to detour the address lines A13, A14 and A15 and the R/W line by using a 157 multiplexer: the output is connected to the original lines on the board, side A is connected to the mentioned lines of the CPU and side B is connected to +5V. The moment you address anything that isn't on the original board but on your board, you switch the 157 to side B and the original board starts to read from the original Kernal or underlaying RAM. (Why the Kernal? Any 'safe' address can do. Reading the VIC could wipe information you could need later and therefore I don't consider that as a safe address) To avoid bus collisions, add a 245 bi-directional buffer in the data bus between the original board and yours. Use a PAL/GAL to tell the 157 when to detour the original signals or not. If you use a CPLD, you can incorperate the mentioned 157. You want more Kernals, different CHARROMs and/or BASICROMs as well? Place them on you board! You can program the GAL/CPLD in such a way that the system starts up from the ROM on your board: there you have your menu. And your menu enables you to choose the wanted Kernal, or whatever, by manipulating the 6526. Adding extra RAM in the demirrored area has its advantages: when a certain value has been read from a reserved place, the menu program skips itself and starts up a pre-choosen Kernal. One more idea: connect the NMI and/or IRQ line to the CPLD and start emulating freezers and other carts! I hope this was clear enough :) -- ___ / __|__ / / |_/ Groetjes, Ruud \ \__|_\ \___| URL: Ruud.C64.org 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. APG Algemene Pensioen Groep NV is gevestigd te Heerlen en is ingeschreven in het handelsregister van de Kamer van Koophandel Limburg onder nummer 14099617 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 it's 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. APG Algemene Pensioen Groep NV is registered in the trade register of the Chamber of Commerce Limburg, The Netherlands, registration number: 14099617 Message was sent through the cbm-hackers mailing listReceived on 2012-05-16 07:00:05
Archive generated by hypermail 2.2.0.