DESCRIPTION
INPUTS
2 - 2
WBPEEUI240752A0
®
Input signal path and low isolation capacitance allow protec-
tion against fast transient-burst disturbance.
The threshold detection block circuits test the input voltage to
determine if it is at the proper voltage level to indicate an ON
or OFF state. The output of this comparator is sent to a read
buffer in the control logic block. If an input is energized, it also
causes a corresponding input status LED on the front panel to
light.
The control logic block consists of buffers that hold the input
and status byte values. The I/O expander bus interface allows
the control module to read these bytes.
Input Circuit Description
When an input signal is present at the proper voltage level, a
zener diode conducts (turns on) to cause current flow through
an optocoupler. Configurable jumpers (on IMDSI12) or fixed
resistors (on IMDSI13, IMDSI14 or IMDSI15) select the
turn-on threshold and input voltage.
The optocoupler output causes a comparator output to go low.
This lights a corresponding status LED on the module front
panel to indicate an energized input; the I/O expander bus
interface transmits a logic 1 to the control module on the I/O
expander bus. When no input signal is present, no current
flows through the optocoupler. The front panel LED does not
light and the DSI transmits a logic 0 on the bus. Figure
shows the digital input circuit.
NOTE: The components inside the dashed boxes in Figure
are
mounted only on the module versions stated in the note.
Figure 2-1. Digital Input Module Block Diagram
LOGIC
POWER
FIELD
INPUT
THRESHOLD
DETECTION
CONTROL
LOGIC
ADDRESS
SWITCH
MODULE
STATUS
GROUP A
LEDs
GROUP B
LEDs
I/O EXPANDER
BUS INTERFACE
GROUP A
GROUP B
I/O
EXPANDER
BUS
P1
P3
P2
TP65206B
S1
1
OPEN
8
INPUT
ISOLATION
