SMART I/O User’s Manual
March 12, 1996
©1996 PEP Modular Computers GmbH
Page 4 - 8
Chapter 4 Digital Modules
4.1.5 Functional Description
Figure 4.1.5.1: SM-DIN1 Schematic Diagram
The input circuit comprises a Zener diode requiring 3mA to drive it beyond
the ‘knee’ that borders between ‘OFF’ and ‘ON’. More simply, input
voltages between 8V and 10V DC produce an unknown digital result.
After the optoisolation part of the circuit, an R-C first-order, low-pass filter
prevents noise and signals greater than 200Hz from entering the system
digital input. This filter is factory set on all channels but may be altered to a
value according to customer specifications.
The LED driver activates the relevant LED when the input exceeds 10V DC.
As previously mentioned, the last channel is capable of issuing IRQx inter-
rupts when enabled by software. This interrupt will only be acknowledged
under OS-9 if the module is on the SMART-BASE or occupies the first slot
of the first attached SMART-EXT unit. This channel is factory set at 200Hz
but higher frequencies may be catered for. The table below shows the solder-
jumper settings for this filter configuration.
+Vcc (24V)
Gnd (common)
Low
Pass
Filter
Digital
Input
LED
Driver
System
Interface
Input
Circuit
User/Input
Interface
System
Interface
Jumper S e t t i n g s
Description
J1
1-2
Standard input filter 200Hz
1-3
Customer specific input filter
J2
1-2
Standard input filter 200Hz
1-3
Customer specific input filter
