The Discrete Input (DI) function block accesses a single discrete value with status input from a two-state field device and makes the processed physical input available to other function blocks. You can configure inversion and alarm detection on the input value.
The Discrete Input function block supports block alarming, mode control, signal status propagation, and simulation.
Normally, the block is used in Automatic (Auto) mode so that the process variable (PV_D) is copied to the output (OUT_D). You can change the mode to Manual (Man) to disconnect the field signal and substitute a manually entered value for OUT_D. In this case, PV_D continues to show the value that will become OUT_D when the mode is changed to Auto.
To support testing, you can enable simulation. This allows the measurement value to be supplied manually or from another block through the SIMULATE_IN_D input.
SIMULATE_IN_D is the simulated discrete with status value used by the block when simulation is enabled.
OUT_D is the discrete output value and status.
The following diagram shows the internal components of the Discrete Input function block:
