Abstract: A bill validation and change system for a slot machine. The system accepts bills of a plurality of denominations and pays out change for the bills in coins of the denomation which may be accepted by the slot machine to play a game. Coins input to the slot machine are stored in a coin hopper which is controlled to payout coins to game winners and to make change for bills. The system includes a master processor which determines winning game plays and whether change for a bill should be made. The master processor further controls the coin hopper to payout coins to winners and to make change for a bill. The master processor is coupled to a slave processor which in conjunction with a bill input device determines the validity and denomination of a received bill. The slave processor controls the bill input device to accept valid bills for which the master processor determines that change should be made and to reject other bills.