There are 6 signals going from the Mega II to the slotmaker.
I had a look at these with a logic probe and found the logic states
shown below on the slotmaker when accessing the slot rom.
I used the following code to loop while checking the logic state, just
change 803 to the address of slot Rom to check.
800:78 SEI
801:AD 0 C1 LDA $C100
804:4c 0 8 JMP $800
P - Pulse
Pin Def State Slot1 Slot2 Slot3 Slot4 Slot5 Slot6 Slot7 C800-CFFF
6 -> L PH L PH L PH L PH L
7 -> L L PH PH L L PH PH L
8 -> H PL PL PL H H H H
PL
9 -> H H H H H H H H
H
10 -> L L L L L L L
L L
11 -> H PL PL PL PL PL PL PL PL
Hope this helps