Nortel Millennium Phone: Coin Acceptor

There are quite a few chips on the coin acceptor mechanism, including what looks like a custom Motorola microcontroller. It is not a simple switch for each coin type and relay for accept/return of coins. There appears to be some sort of elctromagnetic sensow to read the coin type, a solenoid to reject non-valid coins immediately, and a servo to rotate the hopper into the coin return/coin keep areas.
Given that most of the 10 pins are connected to ground, and there are at most 4 pins to work with, I am guessing there is some sort of serial communication to control the coin mechinism from the main board.