DESCRIPTION AND OPERATION
FUNCTIONAL BLOCK DIAGRAM
I-E96-310B
2 - 3
Output Control Logic
An output register holds the output data that is sent to the
solid state relays. The I/O expander bus interface writes con-
trol module data to this register. This data, sent to the data
selector block, sets the relay states for normal operation.
Default data from the control module is sent to the default reg-
ister. The control module configuration sets the default values
(function code 128). The default register is reset to logic zeros
during power up to drive the output relays to a de-energized
state. Function code 128 in the control module configuration
selects the output values used to drive the output circuits in
the event of a control module failure (time-out condition). If
function code 128 is not defined, the outputs will go to a
de-energized state during a time-out condition. Refer to
for further explanation of a time-out condition.
The default control logic block is a one-bit latch register. It
sends a signal to the data selector block to select either the
default register data or the output register data during a
time-out condition (indicating a control module error). This sig-
nal is dependent on the control module configuration (function
code 83, specification S2). The bus fault detector in the I/O
expander bus interface checks for a time-out condition. During
a time-out condition, the data selector block normally selects
the default register data. If a hold option is selected in function
code 83, the control logic block sends a logic one to override
the data selector. It causes the data selector to drive the relays
with output register data instead of default data to maintain
the outputs at their current values.
Status Logic
Optocouplers in the fuse status detector block isolate the digi-
tal outputs from the I/O module circuits. The fuse status
detector block also has circuits that test the individual fuse
conditions to indicate a blown (open) or good fuse. This block
sends the individual fuse state signals to a status buffer and
an OR gate. Blown fuses cause the OR gate to output a signal
that lights the front panel blown fuse LED indicator. It also sets
a bit in a status buffer to indicate to the control module that
the fuse LED is lit.
When field and power wiring are connected to the appropriate
termination unit or module, the blown fuse detection circuitry
is enabled in IMDSO01 modules. For IMDSO02 and IMDSO03
modules, the blown fuse detection circuitry for each output is
operational only when the solid state relay of the output is
energized. The energized relay provides a current path for the
isolated I/O supply voltage that drives the blown fuse detection
circuits. When a fuse blows, it is detected by the circuits and
latched. This latched output lights the front panel fuse status
