DESCRIPTION AND OPERATION
INPUTS AND OUTPUTS
2 - 2
I-E96-309A
®
Input Circuit
Figure
shows the DSM block diagram and signal flow
through the module. The input isolation block consists of cur-
rent limiters and optocouplers to isolate the sixteen field inputs
(or outputs) from the module circuitry. The input circuits pro-
vide 150 VDC isolation between input and logic circuits, and
other input channels.
The isolated outputs are sent to a read buffer in the control
logic block. If an input is energized, it also causes a corre-
sponding 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 slave expander bus interface
allows the master module to read these bytes.
Input Circuit Description
When the DSM uses an I/O point as an input, a signal from the
controlling master controls the logic level of the circuit's signal
line.This external signal may set the line to logic common (0 VDC)
or to logic high (24 VDC). When the input signal is low, current
flows through the input circuit. Other circuitry in the DSM senses
the current flow, lights the front panel LED that corresponds to
the I/O point, and passes a logic 1 to the module. When a signal
is high, no current flows through the input circuit. The front
panel does not light and a logic 0 passes into the module.
Output Circuit Description
When the DSM uses an I/O point as an output, the module
controls the logic level of the signal with a transistor. The tran-
sistor energizes to switch the signal line low. The front panel
light associated with the I/O point lights and the module out-
puts a logic 1. When the transistor is not energized, the cir-
cuitry sets the signal line high. The front panel LED for the I/O
point does not light and the outputs a logic 0.
NOTE: During a power on reset of the DSM such as during installa-
tion, before reconfiguration, or after a power outage, the module
latches all outputs off if the configuration switch is set to hold values
on default. The outputs remain off until a master re-establishes com-
munication with the DSM. The outputs go to preprogrammed default
states if both the master module is active and the configuration
switch is set to go to the preprogrammed state on default.
shows a typical I/O circuit.
Input Circuit Connections
The contact input signals connect to the 30-pin card edge con-
nector P3 (shown in Figure
), using a termination cable
from a termination unit or module.
