Pepper Computer Modular Computers RS485 - Manual (Page 109)

SMART I/O User’s Manual
©1996 PEP Modular Computers GmbH March 12, 1996 Page 4 - 21
4
Chapter 4 Digital Modules
4.2.5 Functional Description
Figure 4.2.5.1: SM-DOUT1 Schematic Diagram
The system interface is low active which means that a logical ‘0’ activates
the LED and optoisolation stage causing the output to switch the 24V Vcc to
power the load.
The driving output device is a Darlington transistor pair protected against
inductive loads by an additional clamp diode. Furthermore, because each
output stage requires three terminals to remain independent and only 14 such
terminals are available, the common Vcc and GND lines have been grouped.
Hence, each pair of outputs is coupled to one Vcc line and to each pair of
Vcc lines is one ground.
Warning !
Individual outputs should not be cascaded as it cannot be guaranteed that
power sharing will be proportional due to the transistor characteristics.
Load
+Vcc (common)
Gnd
LED
Driver
Digital
Output
System
Interface
Output
Stage
System
Interface
User/Output
Interface