Our intelligent Blood Bowl game board consists of two PIC micros which talk to each other via serial (during testing we're using 9600 baud but will crank this up for the final version). The slave board is simply a 40-pin 16F877A with pull-down resistors on all the digital i/o pins.
To allow for maximum flexibility, we're designing this slave board to accept as wide a range of PIC microcontrollers as possible, including some of the 18F series chips (if you have some hanging around from other projects, why not use them instead of buying in new?) Allowing for the power, ground, TX and RX pins (which are in the same place in the 40-pin 16F and 18F chips), as well as the useless Vusb pin on the 18F (useless in this case since we can't use UART and USB together) and the handshaking line we've got a maximum of 30 input pins (we could use the RX pin for handshaking, but for now we'll keep that clear in case we can come up with a use for it in future). In the diagram above, all available i/o pins have been taken out to a set of SMT (1206 sized) resistor pads, and all the resistors are tied to ground (making them pull-down resistors on each input).
30 inputs is an awkward number to work with since each board module is 4 squares in size the maximum number of inputs we can use is 28 (4*7=28). So we've got two free input pins on the slave board should the need arise, as we develop the concept further.