I've never seen a 128KB mod. I suppose it must be doable tho, there're neither new data lines nor differences between old & new IC's. No need to rewire anything except a new /CAS line (am I right?)
I really wonder if one can simply piggyback a new pair of 4464 and let the MSX mapper do the rest...
I really wonder if one can simply piggyback a new pair of 4464 and let the MSX mapper do the rest...
Normally, as long as the mapper has the extra /CAS signals already available, yes. Lift pin 16 and connect.. You need the service manual or the MB670836 datasheet probably though..
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Yes, but I would like to see 512KB, I know some1 did but the diagrams are long gone.
So the F1XDJ also has the S-1985 engine? In that case the mapper logic of it could be used (it has a 5 bits or 512kB mapper).. However I don't know how the MB670836 is connected to the S-1985 and if it'll interfere.. need schematics..
I would also love to find a F1XDJ schematic, never found the slightest info tho. The MB670836 seems to be also a total mistery. Only pin43 seems to be identified as /CAS1 (I suppose). A pity.
The HB-F1XV uses a MB670836 for the mapper logic, so it needs an additional TTL in order to address 512KB, plus a diode, and of course, double the RAM (4x44256).
RAMs are then connected pin-a-pin (piggy back) in pairs, except for /OE and /WR (pins 1 and 4 on 4464). Or pins 16 (/OE) and 3 (/WR) on 44256.
So the refresh state remains untouched, a TTL just redirect read & write from bank select (RAM) to another just checking MA18 state. However to activate MA18 on S-1985 you'll need to add a diode on X5 line from keyboard matrix.
The diagram was lost forever. The TTL in question wasn't mentioned too (only on diagram), but wouldn't be hard to figure out which can works in this way.
