I also had a AM29F040B 4Mbit (512kb) flash chip and I also wanted to replace the roms in my QL to add TK2 and Minerva. Because this chip is 8 times bigger than QL roms + TK2 (64Kb) I made the following circuit that can be used to choose one of 4 different rom sets to boot the QL from. It borrows one of the not used gates from the ram upgrade circuit and uses 2 togle switches for rom set selection.
This is the Ram upgrade + the rom selection circuit:
- added some info
By removing the original rom chips I was able to house the 684000 ram chip into IC33 socket and the AM29F040B into the IC34 socket of course after bending the pins that do not match and connecting them using wires to the correct signals. One can use a 2Mbit eprom instead of the large flash chip that I used or a 1Mbit for 2 rom sets-one switch.
I programmed the JS rom from 0000 to BFFF, the TK2 from C000 to FFFF, Minerva from 10000 to 1BFFF, Tk2 again from 1C000 to 1FFFF and so on with the greek rom+tk2 as the third set and finally the GST 68K/OS.