National Instruments 653X - Manual (Page 112)

Appendix D Hardware Considerations
653X User Manual 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. National Instruments
does not specify the source or input impedance or slew rate of the
653X device or the characteristic impedance of the SH6868-D1 cable.
However, the following information might be helpful:
• I/O buffers—The DIO-32HS uses 24 mA rate-controlled TTL-level
CMOS drivers that provide a low output impedance (<20
Ω typical)
and a high input impedance (limited by the onboard bias resistors of
2.2 k
Ω for control lines and 100 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)