Appendix D
Hardware Considerations
D-8
ni.com
Figure D-5.
Transmission Line Terminations
Note
Run the signal lines through special metal conduits to protect them from magnetic
fields caused by electric motors, welding equipment, breakers, or transformers.
If you are using the Schottky diode termination scheme, you do not need to
know the exact input, output, or cable impedances. NI does not specify the
source or input impedance or slew rate of the NI 653
X
or the characteristic
impedance of the SH6868-D1 cable. However, the following information
might be helpful:
•
I/O buffers—The NI 653
X
uses 24 mA rate-controlled TTL-level
CMOS drivers that provide a low output impedance of 10
Ω
(typical)
and a high input impedance limited by the onboard bias resistors to
2.2 k
Ω
for control lines and 100 k
Ω
for data lines.
•
Slew rate—The rate-controlled outputs have been deliberately slowed
to reduce termination difficulties. Rise or fall time depends on load, but
2.75 to 4.5 ns is typical.
+5 V
+5 V
+5 V
653
X Device
Peripheral Device
Data Control Line
(Input)
Data Control Line
(Output)
Data Control Line
(Output)
