3
Windows Driver
DTR off
Compare the slider of RTS off.
DSR enable
Enables transmission control via the DSR input.
RS 485 operation
RS 485 very often uses a shared medium (one pair of wires) to send and receive
data. This requires the ability to disable the transmission unit. It must be off to receive data, and
must be switched on when transmitting. After transmit is finished it must be off again as soon
as possible.
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Very often this switching is controlled via signals like RTS or DTR. But in many
environments it is difficult for an application to do this in a reasonable time. Now this option can
help.
Figure 21: Auto-DTR Modes
The UART controls the DTR by itself. As long as data is in the transmission FIFO the DTR
signal is held High (or Low). When the transmission FIFO is empty the DTR changes. An
external converter may monitor this signal to act as needed.
RS 485 usage can be compared to communication over handheld transceiver, many people are
familiar with this. To talk one has to press a button. If two or more persons talk at the same time,
no one can hear clearly. For listening the button has to be released. Now the DTR operates like an
“automatic” button, which presses itself as soon as one starts to talk. And it releases afterwards
while the user is silent.
This feature is very useful for older applications. Often there are applications written for a half-
duplex protocol
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over RS 232. Now this must operate over a longer distance. So RS 485 is chosen
to transmit the data. But the application does not know about this, and does not control the RTS
or DTR signal. The driver can do this invisible to the application.
3.3 Windows NT 4.0
Windows NT 4.0 is different from Windows 2000 up to the latest versions of Vista, and also the no
longer supported
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strand of 9x systems (Windows 95 up to ME). These other are all Plug & Play
systems, meaning they will detect
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added hardware themselves. Users are asked to provide the
required driver files. In Windows NT drivers are installed, and fail to load if the hardware is not
available.
The VScom drivers for Windows NT implement the Plug & Play functions in a limited sense. There
is a supervisor utility, restricted to detect VScom PCI cards.
5
Think of it as talking by Walkie-Talkie
6
XMODEM and YMODEM are good examples
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By Microsoft that is, they ceased support for all versions up to Windows 2000
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You may even configure the hardware via Windows
February 2010
VScom PCIex Card User Manual
31
