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. ThisFigure 4.2 - Solid State Input 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 4.3 - Isolated Mechanical Input
Figure 4.1 - Switch Input
| 17 | 18 |
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B&B Electronics |
| B&B Electronics | |
PH (815) |
| PH (815) | |