Positive or Negative Inputs

Inputs for this module can be either positive or negative inputs (all 16 inputs must be the same

type). Both types of signal produce a logic 1 (true) when the switch is closed. Selection of

positive or negative operation is made by the manner in which the external power supply is

connected to the inputs and to the I/O Terminal Block.

Positive inputs receive current from input devices and supply current to the common or negative

power bus. Input devices are connected between the positive power bus and the input terminals.

Negative inputs provide current to input devices and accept current from the common or

positive power bus. Input devices are connected between the negative power bus and the input

terminal.

A network of resistors and capacitors establishes input thresholds and provides input filtering.

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

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±seri al converters change input data from the data buffer into the serial format

needed by the Bus Interface Unit.