On Sat, 20 Nov 2010, Jim Brain wrote: > An English translation of the article would help clarify... The explanation is on page 7, but rather wordy, so I restrict it to the technical content: The module needs to know whether ROM or RAM configuration is used for Kernal accesses in order to properly bank-in the external ROM. However, that information is not present on the Expansion port. Hence, the cartridge simulates a module in the BASIC space. Whenever the VIC doesn't fully use its bus cycle (i.e. phi2=0, bus available). Then the "bus-free controller" starts (BF=0) and toggles a memory configuration according to figure 6. The address manager (AM) then responds with an according HIRAM setting which is stored in a flipflop within the RAM/ROM control (and signalled via LED D2). Whenever CPU or VIC signal bus access, BF=1 occurs it is checked whether a VIC access takes place (nothing happens here) or a CPU access: in that case, the Kernel-select Unit (KSU) checks whether it is an access to Kernal address space (signals HIRAM, Remote/RM). Upon positive check, GAME is pulled low (using Access Request/AR) and the cartridge is banked in. The AM respons with an according ROMH setting which the Kernal-access Control (KAC) combines with Kernal Select (KS) in order to ensure that no Kernal access takes place for accesses to the $A000 to $BFFF range. The resulting control signal (ROMH plus KA) is buffered and fed into the EPROM's OE signal. If the processor is done reading the external Kernal, KSU detaches (AR=1) and the previous memory configuration is restored. Further care is taken in order to avoid interference with external modules, hence GAME and EXROM will only be switched through upon an access to Module memory space. Likewise, ROMH signaling to some further module must only occur if the corresponding memory address range is selected, i.e. no Kernal access takes place. The circuitry therefore consists of the Kernel-Access Detector (KAC), the Select Logic (performing glitch- and crash-free switching among the 4 EPROMs), the "Interface for more expansion" enabling further modules in the $8000 to $BFFF space, Write-enable Control (for RAM write access in slot #3) including power fail circuitry. HTH, Rainer Message was sent through the cbm-hackers mailing listReceived on 2010-11-21 15:00:14
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