B&B Electronics RS-485 Digital I/O Module 485SDD16 - Manual (Page 11)

485SDD16-1005 Manual 17
B&B Electronics -- 707 Dayton Road -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 433-5104
Chapter 4 - I/O Interfacing
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 485SDD16 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.
Digital Inputs
As stated earlier, digital input lines are CMOS/TTL compatible
and can only handle voltages from 0Vdc to +5Vdc.
Digital inputs are 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 an I/O line, defined as an input,
senses a voltage level above +2.0Vdc it will be considered "HIGH"
and it's input state will be read as a "1". Conversely, when an input
senses a voltage level below +1.0Vdc it will be considered "LOW"
and it's input state will be read as a "0".
Inputs can also be used to sense AC voltages by using
mechanical or solid state relays. Solid state relays are available
from many manufacturers.
Figures 4.1 - 4.4 show examples of some typical input interfaces.
Figure 4.1 - Switch Input
18 485SDD16-1005 Manual
B&B Electronics -- 707 Dayton Road -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 433-5104
Figure 4.2 - Solid State Input
Figure 4.3 - Isolated Mechanical Input