2.4. Isolated Input
Reading the isolation input register will identify the digital input state of the
photo-couple (isolation input). Figures 2-3 and 2-4 show the basic circuit of the digital
input.
Figure 2-5. Basic Digital Input Circuit.
5 ~ 24 V
AC/DC
Switch
DIA 0
DIB 0
If the AC signal is
used, pins 2-3 of JP1
must be shorted.
Internal
Circuit
Although the normal input voltage range is 5 to 24 V AC or DC, the input can
still be increased to a larger range by choosing suitable external resistors. The
following figure shows how to connect to a larger input. Please note that the input
current should be limited to between 2 mA to 20 mA; too large input current will burn
out the internal resistor Ri, while an input current that is too low will not activate the
photo-coupler isolator. Calculate the input voltage and current, and then replace the
resistor Ri.
PC - 354
R
i = 1.2 K
Ω
/1 W
I
f 20mA
Vin
Onboard circuits
External Circuit
Figure 2-6. Isolated Digital Input Circuit
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