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Full Discussion: Serial Lines Explained
Top Forums UNIX for Dummies Questions & Answers Serial Lines Explained Post 302930455 by sreyan32 on Sunday 4th of January 2015 11:15:36 AM
Old 01-04-2015
Okay from what I have read in this thread I can understand that in the older days you would have a monitor and a keyboard with a serial port connecting to the central CPU. You would communicate with the CPU using signals sent via the serial port. I know this is an over simplification but is it correct ?

Can someone explain how serial ports can be used for session control in a little more detail ?

What baffles me is that is why still use serial ports ? Why not remove them ? On a normal desktop or laptop serial ports are not used the way they were used back in the olden days, so keep them ?

For example as Corona688 mentioned in a earlier thread
stty still gives the baud rate. This is not required so why still keep it.

Why adopt an old standard forcefully when it is not required is my point
 

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PCWEASEL(4)						   BSD Kernel Interfaces Manual 					       PCWEASEL(4)

NAME
pcweasel -- Support for the PC-Weasel serial console board SYNOPSIS
pseudo-device pcweasel weasel* at pci? dev ? function ? Note that the appropriate display device must also be enabled. See pcdisplay(4) for more information. DESCRIPTION
The PC-Weasel is a serial console board for use primarily on Intel-based PC-class systems. It addresses a problem that nearly everyone who has deployed a PC-class server has experienced: the total lack of remote management capability on PC-class hardware. In addition to serial console support, the PC-Weasel provides the ability to remotely reset the system (by means of a hardware reset signal), and provides a watchdog timer function. The PC-Weasel works by emulating the original IBM Monochrome Display Adapter (MDA). Writes to the display's character cells are translated into ANSI terminal sequences which are then sent out the PC-Weasel's serial port. Incoming characters are translated into PC keyboard scan codes and then fed (by means of a cable) into the system's keyboard controller. The system believes it is using a display console. This is particularly important in the event that one needs access to BIOS configuration menus. The PC-Weasel also includes a ST16550 serial port, which may be configured as any one of the system's serial ports. Typical usage is to con- figure the port as com0 at ISA I/O address 0x3f8. When the PC-Weasel detects activity on the ST16550, the serial port is automatically con- nected to the ST16550 so that the serial port may be used as normal. When the PC-Weasel detects activity on the internal UART used for MDA emulation, the serial port is automatically reconnected to the emulation UART. This allows the boot program and kernel to be configured to use the serial port directly (which is more efficient than using the MDA emulation mode), yet allows the MDA emulation to be reestablished as soon as the kernel loses control of the system. The pcweasel driver provides support for the additional features present on the PC-Weasel. At the moment, this includes support for the watchdog timer function. Use of the pcweasel driver is not required in order for the system to function with a PC-Weasel installed so long as only the MDA emulation and ST16550 serial port functionality is required. SEE ALSO
pcdisplay(4), wdogctl(8) HISTORY
The pcweasel driver first appeared in NetBSD 1.5.1. AUTHORS
The PC-Weasel was invented by Herb Peyerl and Jonathan Levine at Canada Connect Corporation. It is now produced by Middle Digital, Inc., http://www.realweasel.com/ The pcweasel driver was written by Jason R. Thorpe <thorpej@zembu.com>, and contributed by Zembu Labs, Inc. Herb Peyerl of Middle Digital, Inc. provided several firmware updates during the development of the driver. BSD
November 23, 2007 BSD
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