> Three month ago I made a simple 32 KB-expansion for someone piggy-backing a > 62256 (32*8KB SRAM) on top of the BASIC-ROM. A 74LS21 (dual 4-input AND) > took care of ANDing the RAM and BLK-lines (not BLK5 !). [..] > there is interest, I'll make a SCH in GIF and check it with Pasi to see if > this is what he had in mind. Not quite, because for a cartridge you need to generate A13 and A14, because they are not available in the cartridge port. My thought was to use quad 2-input AND to generate the address bits and the chip select for the RAM. Okay, I'll sketch the connection here.. _ +---| \ | | )-------------- A13ram | +-|_/ H | | _ /B1 --o o-+---+-| \ H | | )----+--------- A14ram /B2 --o o-+-----|_/ | _ H | _ +--| \ /B3 --o o-+-+---| \ | )--- /CSram H | )-------|_/ /B5 --o o-+-----|_/ VR/W ---o H o-+--- R/Wram CR/W ---o H is a pullup resistor, 100-470kOhm should work fine. --o o-- is a place for a jumper block or a switch. You should also add ~100nF capacitor between VDDram and GNDram. You can disable all blocks separately and write-protect the whole thing by removing jumpers. If you use this style, it would be usable for both internal and external expansion. -Pasi -- /His hands almost went to his ears in a strangely human gesture. Like a boy he looked, almost lost. God, that our immortal bodies could be such varied prisons for us, that our immortal faces should be such masks for our true souls./ -- Lestat in "The Vampire Lestat" - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail email@example.com.
Archive generated by hypermail 2.1.1.