Appendix B Serial Port Information
Serial for Windows NT
B-6
©
National Instruments Corporation
Figure B-4 shows a transmission line using bias resistors.
620
Ω
Bias Resistor
+5
A
Tx
B
620
Ω
Bias Resistor
100
Ω
Termination Resistor
Figure B-4.
Transmission Line Using Bias Resistors
Rather than using two 620
Ω
resistors at one node, you can also increase
the value of the resistors and put them at every node. For instance, if
there are eight nodes in a system, you can use 4.7 k
Ω
resistors at each
node to effectively achieve the same result.
DTE vs. DCE
Data Terminal Equipment (DTE) and Data Communications Equipment
(DCE) were the terms used in the RS-232 specification for the types of
equipment on either end of a serial connection. (A DCE is called Data
Circuit-Terminating Equipment in Revision D of the RS-232
specification.) In general, DTE and DCE refer to computer equipment
and modems, respectively. Because the RS-232 specification mainly
involves connecting a DTE directly to a DCE and vice versa, the pinouts
are defined so that cabling is simple. That is, a cable connected a
computer to a modem by wiring pin 1 to pin 1, pin 2 to pin 2, and so on.
This method is commonly known as straight-through cabling.
