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UART(4)			 BSD Kernel Interfaces Manual		       UART(4)

NAME
     uart -- driver for	Universal Asynchronous Receiver/Transmitter (UART) de-
     vices

SYNOPSIS
     device uart

     device puc
     device uart

DESCRIPTION
     The uart device driver provides support for various classes of UARTs im-
     plementing	the EIA	RS-232C	(CCITT V.24) serial communications interface.
     Each such interface is controlled by a separate and independent instance
     of	the uart driver.  The primary support for devices that contain multi-
     ple serial	interfaces or that contain other functionality besides one or
     more serial interfaces is provided	by the puc(4) device driver.  However,
     the serial	interfaces of those devices that are managed by	the puc(4)
     driver are	controlled by the uart driver.	As such, the puc(4) driver
     provides umbrella functionality for the uart driver and hides the com-
     plexities that are	inherent when elementary components are	packaged to-
     gether.

     The uart driver has a modular design to allow it to be used on differing
     hardware and for various purposes.	 In the	following sections the compo-
     nents are discussed in detail.  Options are described in the section that
     covers the	component to which each	option applies.

   CORE	COMPONENT
     At	the heart of the uart driver is	the core component.  It	contains the
     bus attachments and the low-level interrupt handler.

   HARDWARE DRIVERS
     The core component	and the	kernel interfaces talk to the hardware through
     the hardware interface.  This interface serves as an abstraction of the
     hardware and allows varying UARTs to be used for serial communications.

   SYSTEM DEVICES
     System devices are	UARTs that have	a special purpose by way of hardware
     design or software	setup.	For example, Sun UltraSparc machines use UARTs
     as	their keyboard interface.  Such	an UART	cannot be used for general
     purpose communications.  Likewise,	when the kernel	is configured for a
     serial console, the corresponding UART will in turn be a system device so
     that the kernel can output	boot messages early on in the boot process.

   KERNEL INTERFACES
     The last but not least of the components is the kernel interface.	This
     component ultimately determines how the UART is made visible to the ker-
     nel in particular and to users in general.	 The default kernel interface
     is	the TTY	interface.  This allows	the UART to be used for	terminals,
     modems and	serial line IP applications.  System devices, with the notable
     exception of serial consoles, generally have specialized kernel inter-
     faces.

SEE ALSO
     puc(4)

HISTORY
     The uart device driver first appeared in FreeBSD 5.2.

AUTHORS
     This manual page was written by Marcel Moolenaar <marcel@xcllnt.net>.

BSD				August 25, 2003				   BSD

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | HISTORY | AUTHORS

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