A current ATM exchanger consists of ATM switch and ATM interface card is implemented with many LSIs. An investigation of an architecture of the ATM interface card is, therefore, important to decides ATM exchanger's functions and its flexibility. In this paper, we propose an architecture of the ATM interface card to contribute to improving the flexibility and reducing the cost for an ATM exchanger. The key feature of the proposed architecture is both physical layer and ATM layer functions at an interface point are executed by a general-purpose microprocessor and FIFOs. A realization of such architecture is discussed, especially, a software configuration of it is proposed because the physical layer functions have to be executed periodically and should not be interrupted. We developed an evaluation breadboard for such periodic software execution and evaluated the proposed ATM interface card architecture. The evaluation results indicate that a 50 MHz R3000 microprocessor and 5 MHz access speed FIFOs can realize the 6.3-Mbps cell relay interface card.