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232 CHAPTER NINE
generally considered serial links. Many computer boards come already wired with these
sorts of communication ports, and many interface chips are available that support them.
RS232/423 RS232/423 has been around since 1962 and is capable of sending
data at up to 100 Kbps (RS423) over a three-wire interface. It is considered to be
a local interface for point-to-point communication. It’s supposed to be simple to
use, but it can cause a considerable amount of grief because many optional wires
and different pinouts exist for various types of connectors. Other than the physi-
cal layer and the definition of bit ordering, very little layering takes place above
the physical layer with RS232. For more info, go to www.arcelect.com/rs232.htm
and www.camiresearch.com/Data_Com_Basics/RS232_standard.html.
RS422 RS422 uses differential, balanced signals, which are more immune from
noise than RS232’s single-sided wiring. Data rates are up to 10 Mbps at over 4,000
feet of wiring. Other than the physical layer and the definition of bit ordering, very
little layering is done with RS422 (also see www.arcelect.com/rs422.htm).
10BT/100BT/1000BT networking Ethernet is one of the most popular local
area network (LAN) technologies. 10BT LAN technology enables most business
offices to connect all the computers to the network. The computers can transmit
data to one another at speeds approaching 9 to 10 million bits per second. As a
practical matter, on busy networks, the best rates a user can achieve are much
lower. The software stack includes up to four layers from physical layer 1 (network
interface [NIC] cards), up to IP, and to TCP at layer 4.
100BT is 10 times faster than 10BT. 1000BT is 10 times faster again and avail-
able for use with a fiber-optic physical layer as well as copper wiring. See these
web sites and PDF files for more info:
www.lantronix.com/learning/tutorials/
www.lothlorien.net/collections/computer/ethernet.html
ftp://ftp.iol.unh.edu/pub/gec/training/pcs.pdf
www.10gea.org/GEA1000BASET1197_rev-wp.pdf

Modulated Communications

Sometimes digital communications just cannot be sent over a channel without modula-
tion; baseband communications will not work. This might be the case for several reasons:

Sometimes wiring is not a possibility because of distance. Unmodulated data sig-
nals are generally relatively low in frequency. Transmitting a slower baseband sig-
nal through an antenna requires an antenna roughly the size of the wavelength of