Extron Electronics IPL T SFI244 - Manual (Page 25)

Digital input
When a flex I/O port is configured as a digital input, the port measures two states: 1 or 0;
On or Off; high or low. A closed circuit = a logic 1 and an open circuit = a logic 0.
24K SW1
2K
+30V +5V
SW2
I/O
GND
Figure 16. Equivalent Digital Input Circuit
The Digital Input mode has two configurable options:
1. The ability to turn on an internal pull-up resistor to +5 VDC (shown below as SW2)
2. Adjustable detection threshold voltages
The default threshold voltages follow standard TTL logic: a voltage below 0.8 VDC is
measured as logic low and a voltage above 2.0 VDC is measured as logic high. Using an
adjustable threshold, the integrator can select the proper high and low voltages for the
installation.
NOTE: In the figure below, the SW2 switch is turned closed, activating the +5 VDC and
2K pull-up resistor.
I/O
2K
+30V +5V
SW2
GND
24K
Figure 17. Sample Wiring for a Digital Input Reading an External Pushbutton
Switch
IPL T SFI244 • Communication and Control 19