The CompactBlock I/O 1791P series is a series composed of different I/O blocks that have been manufactured and designed by Allen-Bradley. The main units in the series can be mounted on a machine or they can be installed directly in a cabinet. The Allen-Bradley CompactBlock I/O 1791P series is designed to be used in indoor environments, especially within an IP 20 rated enclosure. The blocks of this series include digital I/O and analog I/O, and they come with temperature detection features that are compatible with a wide variety of sensors and that are intended to be installed in confined spaces. When it comes to communications, these blocks are compatible with the DeviceNet and the Profibus DP network technology. These can be connected to different I/O modules through one of these networks.

The Allen-Bradley CompactBlock I/O 1791P series I/O blocks can be used with 3 different expansion modules, 80 points of I/O for DeviceNet networks, and 64 I/O points for the PROFIBUS DP network. The analog blocks support 2 additional modules with 32 points of digital I/O each. These blocks are easy to connect and configure, and these blocks come with a messaging mechanism that increases productivity and makes them able to work with any DeviceNet scanner. The Allen-Bradley CompactBlock I/O 1791P block uses a network protocol called the I/O slaved messaging protocol that includes the poll command, the bit stroke command, and the cyclic and COS command. The whole series has an isolation voltage rating of 50 Volts DC and these blocks require a wire size of 0.25 to 2.5 millimeters square.