 Turns out I had made a mistake on my TG16 Edge footprint and had reversed A19 and A18. This explains perfectly the behaviour I had seen a few weeks backs. A reversing of A19 and A18 performs a weird remapping of the HuCard memory space in 2Mbit chunks. Last time, all 2Mbit games worked and all 3Mbit games worked too (by pure luck though, as their upper 1Mbit should've been screwy). In fact, I've been using this wrong footprint for quite some time now, though the labelling of A19 and A18 have no impact whatsoever on PC-Henshin and Turbo PC-Henshin because these two devices simple pass-through the address lines.
Luckily, modding the dbCards proved to be quite simple. On 4Mbit or less dbCard, I don't need A19 at all so I simply cut it and soldered a small fly-wire to A18. On 8Mbit dbCard, I do need A19 so this one is a bit trickier. I cut both A19 and A18 and rerouted them individually to their correct location. The 8Mbit card also has a small address decoder to generate chip-select signals for both chips.
 The next steps for this project are that I would like to use a single chip solution instead of the current two chip solution. The only reason this doesn't have the single chip solution is that I only found a suitable 8Mbit 5V Flash (MX29F800C) a few days after having ordered these prototypes. The MX29F800C however will require a small adapter between the TL866CS eeprom burner and the dbCard - I suppose in this sense the two chip design is slightly more elegant - but overall it will be a better and more cost effective design. I also need to consider form factor in order to make the next rev of dbCards more consumer friendly, that is, to eventually make it look and feel similar to a real HuCard. That would probably mean: use a thinner board, mount ICs upside down, make a prototype mould to carry the PCB. The end result should not expose the IC to the user and should look much more like a real HuCard. |
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