Editing COM (hardware interface) (section)

==I/O addresses==
The COM ports are interfaced by an integrated circuit such as [[16550 UART]]. This [[Integrated circuit|IC]] has seven internal 8-bit [[Hardware register|registers]] which hold information and configuration data about which data is to be sent or was received, the [[baud rate]], [[interrupt]] configuration and more. In the case of COM1, these registers can be accessed by writing to or reading from the [[I/O address]]es {{mono|0x3F8}} to {{mono|0x3FF}}. 

If the CPU, for example, wants to send information out on COM1, it writes to [[I/O port]] {{mono|0x3F8}}, as this I/O port is "connected" to the UART IC register which holds the information that is to be sent out.

The COM ports in PC-compatible computers are typically defined as:<ref>{{Cite web |title=22.2.3. Resources Required by Serial Ports - PC Hardware in a Nutshell, 3rd Edition [Book] |url=https://www.oreilly.com/library/view/pc-hardware-in/059600513X/ch22s02s03.html |access-date=2024-10-15 |website=www.oreilly.com |language=en}}</ref>
*'''COM1''': [[I/O port]] {{mono|0x3F8-0x3FF}}, [[Interrupt request|IRQ]] 4
*'''COM2''': I/O port {{mono|0x2F8-0x2FF}}, IRQ 3
*'''COM3''': I/O port {{mono|0x3E8-0x3EF}}, IRQ 4
*'''COM4''': I/O port {{mono|0x2E8-0x2EF}}, IRQ 3