COM Ports on PCsA port can use any addresses and IRQ lines supported by the system hardware.
These are the addresses and IRQ lines allocated to COM ports in early PCs:Older ports often have jumpers, switches, or configuration utilities that enable
selecting a base address and IRQ line. The setup screens that you can access on
boot up can enable configuring motherboard ports. With some hardware, mul-
tiple ports can share an IRQ line.
A port on a USB/serial converter doesn’t have its own addresses and IRQ line.
Instead, the port uses the shared resources of the Universal Serial Bus.!
!8
A serial server is a device that enables accessing serial ports over a network. A
typical serial server contains a microcontroller, an Ethernet controller, and one
or more UARTs that interface to RS-232 or RS-485 ports. The server manages
communications between the Ethernet network and the serial ports. A serial
server can also interface to a wireless (Wi-Fi) network. Many sources offer
serial-server modules.
Serial servers can use defined Internet protocols for network communications.
The specifications are available from http://www.rfc-editor.org.
Most serial servers communicate via TCP (specification STD0007), which
defines a way of establishing a connection to a device and exchanging data with
acknowledgements, sequence numbers, and other features that help ensure reli-
able transfers. Each serial port uses a separate TCP connection. UDP
(STD0006) is an alternative for applications that don’t require TCP’s reliability.
Some serial servers use Telnet connections. The Telnet specification
(STD0008) defines a protocol for transmitting characters and control data over
a TCP connection.
Information specific to COM ports and modems can use protocols defined in
Telnet Com Port Control Option (RFC 2217). This document defines com-
mands for setting COM-port parameters and flow-control methods, reading "#$
COM1 3F8h 4
COM2 2F8h 3
COM3 3E8h 4 or 11
COM4 2E8h 3 or 10