Module Operation

A network of resistors, capacitors, and zener diodes establishes input thresholds and provides

input filtering. Optoisolators provide isolation between the field inputs and the module’s logic

components. An oscillator and switch form a sampling circuit that is transparent to the

controller and the LEDs that indicate the state of the inputs. Data from all 16 inputs is placed

into a data buffer. The module’s circuit LEDs show the current states of the 16 inputs in this

data buffer.

Parallel-to-serial converters change input data from the data buffer into the serial format

needed by the Bus Interface Unit.

After checking the Board ID and verifying that the module is receiving appropriate logic power

from the Bus Interface Unit (which is reflected by the state of the module’s Power LED), the Bus

Interface Module then reads the filtered, converted input data.