Dual Boot R-Type 1 & 2 Arcade PCB - Day 1
Okay here's the rough plan... :/
Use several 74LS157's (Quad 2-input Multiplexer TTL Logic chips), attach all the patch wires involved in the R-Type 1 conversion into all the 'A' inputs..
Then, connect all the original connections (As in the unmodified R-Type 2 configuration) into the 'B' inputs..
Then join the outputs to the motherboard.. and a switch would be fitted to set either game A (or) B (R-Type 1 or 2).
For the main Rom's... I'll use 27c040's where the 27c020's were (and) 27c020's instead of the 27c010's.
- Then take each Rom-image file from RT1 & RT2 (place them 'end-to-end' RT1 in the lower half of the memory & RT2 in the top half (aligned to the relevant 1/2MBit boundary))
.. Then use the A/B select line used above to drive the upper address pin, which will then allow the mother-board to see either of the games data - as per-normal.
(..grounding the select pin you boot RT1 & setting it to 5v will yield RT2) :D
Then do something similar to the sound Rom /or/ Piggy back another 27512 & monkey with the 'Chip Select' lines.. etc.
Okay.. found 10 for £16.23 .. just hope they are fast enough (nano-second wise).