Sorry for the absence in updates. I hope to be posting more frequently in the near future :)
For LD-V1000 operation, I always thought that Dragon's Lair kept the LD-V1000 ENTER line (pin 17, not to be confused with the PR-7820 ENTER line) tied to ground (ie always active). However, I am wrong about this. Looking at the schematics, I just noticed that LD-V1000 Pin 17 is actually tied to the output of an LS374 (an 8-bit latch, called U16 on the schematic). This latch is written to via memory location 0xE008 in the ROM program. This means that the ROM program must actively set bit 7 of memory location 0xE008 to 0 in order for commands to be accepted by the LD-V1000. Setting this bit to 1 would disable command receipt. I actually have no recollection of whether the ROM ever sets this bit to anything other than 0, and , frankly, I can't see any reason to do this since the LD-V1000 (I am pretty sure) has internal pull-ups to force a 0xFF "NO ENTRY" command if no data is put onto the bus during the command strobe window.
Anyway, just something interesting that I never noticed before. The LD-V1000 suggests tying pin 17 to the command strobe (pin 7), but I think tying it to ground would also work.