5. Block Diagram Bus Buffer Timing Channel C Channel D I/O port Control Counter /Timer X2 X1/CLK D0-D7 Internal Bus DUART CD TxDC RxDC TxDD RxDD I/O[3:0]C I/O[3:0]D Interrupt Arbitration IACKN IRQN Operation Control RDN WRN CEN A0-A5 DACKN Channel A Channel B I/O port Control Counter /Timer TxDA RxDA TxDB RxDB I/O[3:0]A I/O[3:0]B DUART AB