Page 87 - DCAP311_DCAP607_WIRELESS_NETWORKS

Unit 5: Wireless PAN Components

late 90’s many computer manufacturers started to phase out the serial COM port in favor of Notes
the USB port. By the mid 2000’s some computers had both a serial COM port and a USB port,
however many did no longer have a serial COM port by that time; and today almost all modern
computers have no serial COM port but only USB ports instead. Since many serial devices with
a RS232, RS485 or RS422 port are still in use and even still produced today, the disappearing of
the serial COM port from personal computers has created a need for the USB to serial adapter.

A USB adapter is a type of protocol converter which is used for converting USB data signals to
and from other communications standards. Commonly, USB adaptors are used to convert USB
data to standard serial port data and vice versa.
Most commonly the USB data signals are converted to either RS232, RS485, RS422 or TTL serial
data. The older serial RS423 protocol is rarely used anymore, so USB to RS423 adapters are hard
to find.
USB to serial RS232 adapters are often used with consumer, commercial and industrial
applications and USB to serial RS485/RS422 adapters are usually mainly used only with
industrial applications.
!

Caution Adapters for converting USB to other standard or proprietary protocols also exist;
however, these are usually not referred to as a serial adapter.
The primary application scenario is to enable USB based computers to access and communicate
with serial devices featuring D-Sub (usually DB9 or DB25) connectors or screw terminals, where
security of the data transmission is not generally an issue.

USB serial adapters can be isolated or non-isolated. The isolated version has opto-couplers and/or
surge suppressors to prevent static electricity or other high-voltage surges to enter the data lines
thereby preventing data loss and damage to the adapter and connected serial device. The non-
isolated version has no protection against static electricity or voltage surges, which is why this
version is usually recommended for only non-critical applications and at short communication
ranges.
As a simplified example a typical standard USB to serial adapter consists of a USB processor
chip which processes the USB signals. The USB processor sends the processed USB signals to a
serial driver chip which applies the correct voltages and sends the processed data signals to the
serial output. For the computer to be able to detect and process the data signals drivers must
be installed on the computer. When the USB to serial adapter is connected to the computer via
the USB port the drivers on the computer creates a virtual COM port which shows up in Device
Manager. This virtual COM port can be accessed and used as if it was a built-in serial COM
port. However, the characteristics of the virtual COM port are not exactly the same as a real
internal COM port, mainly due to data latency; which means that if very sensitive and precise
data transfer is required, the USB to serial adapter might be unreliable and not a desired solution.
Virtual COM drivers are usually available for Windows, Linux and MAC only.

5.4 Wireless Routers

A wireless router is a device that performs the functions of a router but also includes the functions
of a wireless access point. It is commonly used to provide access to the Internet or a computer
network. It does not require a wired link, as the connection is made wirelessly, via radio waves. It
can function in a wired LAN (local area network), in a wireless-only LAN (WLAN), or in a mixed
wired/wireless network, depending on the manufacturer and model.
Most current wireless routers have the following characteristics:

z z One or multiple NICs supporting Fast Ethernet or Gigabit Ethernet integrated into the
main SoC

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