The Allen-Bradley 1791-N4C2 module is a Block I/O analog input/output combination module featuring 4 analog current or voltage inputs and 2 analog voltage outputs. The 1791-N4C2 module features 4 selectable inputs per block. The rated update rate per channel is 108 milliseconds, while the module features an absolute accuracy rating of 0.1% at 25 degrees Celsius. The 1791-N4C2 module is linearity rated at 0.05% at 25 degrees Celsius while the common-mode rejection is set at -75 dB. The module features 2 outputs per block while the output impedance is rated at less than 1 Ohm. The output update rate is 10 milliseconds per output channel, while the module features indefinite short circuit protection.

The Allen-Bradley 1791-N4C2 module comes with different status indicators used to monitor the performance of the unit and allow module troubleshooting. The green indicator shows whether there is communication between the processor or the scanner and the block module. The green indicator light means the unit is powered on and it is running. The 1791-N4C2 module communicates with the processor through a bidirectional block transfer. However, before performing the block transfer, the manufacturer recommends the configuration of the block module. Ensure the blocks have been wired in series and do not attempt wiring the block in parallel. The number of blocks is dependent on the user requirements and also on the system that is used. The termination resistor should be installed on the last block in the series, and the devices not operating at 230.4K baud should have 82-Ohm terminators in place to ensure proper operation.