This small and efficient Input/Output module, the 1791D-4B0, is called a CompactBlock I/O module. Manufactured by Allen Bradley of Rockwell Automation, this I/O module is a part of the 1791D family of CompactBlock devices that contain 4 sinking inputs. This device has many I/O circuits, with a DeviceNet I/O adapter and a built-in power supply. Irrespective of the location, this I/O module could be used anywhere because of its small actuator or a sensor with distributed I/O blocks. It features a NEMA Type 1+ input that allows it to easily exchange data with any kind of sensor at the maximum rate of 500 Kbps for a maximum distance of 100 meters. The 1791D-4B0 also features a protection against any short circuit in the output if miswiring occurs. It has an autobaud detection feature which prevents it from crashing from incorrect baud rate by automatically matching the system baud rate. The proximity of the device to a sensor or actuator also helps bring down the cost of wiring, and, being a compact I/O module, no additional power source or adapter is needed.

The 1791D-4B0 can easily communicate with any SoftLogix controller, or an SLC or a PLC and can possibly act as a slave when in a master/slave condition. One could also select different modes of data exchange in this device like change-of-state, polled, and cyclic. In order to connect the outputs and inputs, a 24 Volt DC power supply is to be used. The 1791D-4B0 can be easily installed on a DIN rail or an enclosed panel and can be mounted either vertically or horizontally. Keep the temperature surrounding of the device in the range 0 to 60 degrees Celsius for optimum performance, and for all wire connections, use a stranded wire with a gauge of 14.