Theory Of Operation - National Instruments SCC-DI01 User Manual

Isolated digital input module

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Theory of Operation

Power-Up Condition

Status LED

Sensing DC Voltages

Sensing AC Voltages

SCC-DI01 Isolated Digital Input Module User Guide

Table 1. SCC-DI01 Module Pin Assignments (Continued)

Pin Number

At power-up, the SCC-DI01 registers a logic low if there are no

connections to the inputs.

The SCC-DI01 has a status LED that indicates when an input signal

registers a logic high or a logic low. The LED is located above the screw

terminals. If the LED is off, the input signal is registering a logic low on the

digital line. If the LED is on, the input signal is registering a logic high on

the digital line.

The SCC-DI01 registers a logic high when a positive or negative

DC voltage of 2 V or more exists across the screw terminals. If no

voltage is present, the SCC-DI01 registers a logic low.

The SCC-DI01 registers a logic high when an AC voltage exists across the

screw terminals. Signals with low amplitude and low frequency cause the

SCC-DI01 to register alternating logic highs and logic lows. Sinusoidal

signals of 1 kHz or higher frequency and 4 V

the SCC-DI01 to register a constant logic high.

Signal Name

—

or higher amplitude cause

rms

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