In the window shown, the
Value pane shows the ???Device description??? property.
Chapter 3
36
A typical COM port on a motherboard or expansion card contains a UART
that interfaces to the system bus, typically a PCI bus. Each UART uses a series
of eight port addresses. The first address in the series is the port??™s base address.
Most of these ports also have an assigned IRQ line to carry interrupt requests.
Ports on motherboards or expansion cards have a Resources tab that displays the port
addresses and IRQ line the port uses. If you uncheck Use automatic settings, you may be
able to change the resources.
COM Ports on PCs
37
A 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, multiple
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.
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