B&B Electronics RS-232 Digital Relay I/O 232DRIO - Manual (Page 17)

232DRIO-0308 Manual 15
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 433-5104
This chapter will explain "HIGH" and "LOW" states and show
some general examples of how to interface to the I/O lines. Caution
must be taken not to exceed 232DRIO specifications listed in
Chapter 1 when interfacing to external devices. Failure to stay
within these specifications could result in damage to the unit and will
void warranty.
Figure 4.1 – Board Layout
Opto-isolated Input
As stated earlier, the opto-isolated input line is CMOS/TTL
compatible and can also handle voltages from 0 to +30 Vdc or Vac.
The isolated input is used to sense a HIGH or a LOW state. This
can be accomplished via switch closures, contact closures, or a
solid state digital signal. When this input senses a voltage level
+5Vdc/Vac or above, it will be considered "LOW" and its input state
will be read as a "0" to the PIC® microcontroller. Conversely, when
an input senses a voltage level below +1.50Vdc/Vac, it will be
considered "HIGH" and its input state will be read as a "1" to the PIC
microcontroller. Correspondingly, the PIC will then evaluate the
incoming input and declare it as a “HIGH” if it is a “0” (at least +5V)
and as a “LOW” if it is a “1” (less than +1.5V).