<P> If the CPU, for example, wants to send information out on COM1, it writes to I / O port 0x3F8, as this I / O port is "connected" to the UART IC register which holds the information that is to be sent out . </P> <P> The COM ports in PC - compatible are typically defined as: </P> <Ul> <Li> COM1: I / O port 0x3F8, IRQ 4 </Li> <Li> COM2: I / O port 0x2F8, IRQ 3 </Li> <Li> COM3: I / O port 0x3E8, IRQ 4 </Li> <Li> COM4: I / O port 0x2E8, IRQ 3 </Li> </Ul> <Li> COM1: I / O port 0x3F8, IRQ 4 </Li>

Which i/o address is used by the com2 port