On 9/17/2012 2:25 PM, Gerrit Heitsch wrote: > >> Ah, well, the '148 option gives you 8 banks to choose from (I used only >> 3, with a sub selection for CHARROM being only 4 kB). Adding more >> options simply means routing the Select lines to another bank select. >> So, with a 3 pin jumper, you can add 2 KERNALs to the design (middle is >> KERNAL select, two ends are two inputs to the '148), but you can add >> more KERNALs as well or BASICs with just more jumpers. > > > > Needs a larger EPROM though. 27C512 for example. Would give you 6 > KERNALs, 1 BASIC and 2 Char-ROM. Yes, if you want all 8 banks in use. BUt, you can just use the lower 4 inputs for a '256. > > I'm looking forward to the finding out how you make the selections work. Well, I sent BASIC, CHARROM into the 0,1 lines of the '148. !GS drives !CE and !OE on the EPROM, while the A and B lines go to the A13 and A14 lines of the EPROM. A12 is handled wither with the NAND gates or the '257, nothing new to report there. Setting up 2 KERNALS means bringing '148 lines 2 and 3 to the ends of a 3 pin header. Middle pin goes to !KERNAL shorting one half will shunt KERNAL to one of the two address lines. It does require 1 more resistor than the '11 solution, as it requires both the 2 and 3 lines of the '148 to be pulled weakly high, but the wiring is simpler. Jim > > Gerrit > > > > Message was sent through the cbm-hackers mailing list -- Jim Brain brain@jbrain.com www.jbrain.com Message was sent through the cbm-hackers mailing listReceived on 2012-09-18 05:00:04
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