Specifications

Digital I/O Functions 6-3
Digital inputs are used to sense switch closures and the state of digital
signals. The inputs are protected to voltages up to ±30V and are normally
pulled up to the logic “1” condition (see Figure 6.3). Digital inputs can be
read by the Digital Input (DI) command. Voltage inputs less than 1 V are
read back as ‘0’. Signals greater than 3.5 V are read as ‘1’. No other
commands have any affect on the inputs.
Switch closures can be read by the digital input by simply connecting the
switch between GND terminal and a digital input. Internal pull-ups are
used so additional parts are unnecessary.
The pull-ups supply only 0.5ma; therefore, self-wiping switches designed
for low current operation should be used. For other types of switches, it
may be necessary to provide extra pull-up current with an external resis-
tor. The resistor should be tied between the switch and +V.
Connection to logic outputs is shown in Figure 6.2. Opto-isolation is used
for isolation and where common-mode exists between the D1000 module
and the signal being sensed.
Digital inputs may be used to sense AC voltages by using isolated sensing
modules offered by many manufacturers.
Event Counter
The Event Counter input is connected to the Digital Input 0 terminal. It can
be used to count any low speed event that occurs on the DIØ/EV input.
Any of the interfacing techniques described for Digital Inputs may be used.
The input pulses must meet the specifications in Figure 6.4 to avoid
missing counts. Switch inputs are filtered to eliminate contact bounce.
Figure 6.3 Digital Inputs