National Instruments 653X Manuale Utente

Figure D-5.  Transmission Line Terminations

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)