Using Discrete Outputs With The Parallel Port - Allen-Bradley A-B QUALITY DL20 Series User Manual

Chapter 7
The Parallel Port
Using the Parallel Port
11A 11B
D9 D8
7–2
Figure 7.2 illustrates a typical example of using discrete I/O outputs with the
DL20 parallel port:
Figure 7.2

Using Discrete Outputs With the Parallel Port

DL20 Parallel Port
12 13 14 15
D7 D6 D5 D4
PC Outputs (12)
Logic Levels
Data line D0 can have a value of either 0 (ground level) or 1 (voltage
present). The convention of having voltage representing a 1 and ground
representing a 0, is known as positive logic. The opposite convention is
known as negative logic. The DL20 can accept either.
Each parallel input understands two voltage levels: On or Off. There is also
an indeterminate state when the voltage level is between On and Off.
Table 7.A shows the voltage levels and their logic values for input terminals
D0-D9 and strobe lines MS0 and MS1.
16 17 18 19
D3 D2 D1 D9
Terminal
21 20 23
Number
MS0 MS1 GND Terminal Block
Designation
-
+
Power Supply
5-30 VDC
(Observe DC
Polarity)