The number of inputs to the LSBFI function block is an extensible parameter. The block default is two inputs.
To add input connectors to the block:
- Select the block diagram.
- Right-click and select Extensible Parameters.
- Modify the number of inputs.
- Click OK.
The Boolean Fan Input function block examines the discrete input values at each block execution. The OUT_INT output is set to the sum of the bit values of the True inputs (IN_D1 is weighted as 1, IN_D2 as 2, IN_D3 as 4, IN_D4 as 8, and so on). The status of OUT_INT is set to the worst status among the inputs.
When FIRST_OUT indicates a trap has not yet occurred (its value is False[0]) and one or more of the inputs have become True, a trap condition is flagged and held by copying the value of OUT_INT to FIRST_OUT. Thereafter, the FIRST_OUT value updates when the IN_Dn values transition from all False (0) to one or more True (1). The status of FIRST_OUT is equal to the status of OUT_INT when the trap occurred. The value of OUT_D is the logical OR of the discrete inputs. OUT_D status is set to the worst status among the inputs.
Once the FIRST_OUT output is reset, the Boolean Fan Input function block does not set it again until all of the IN_D values return to the False (0) state.
To support thumbwheel switch interfaces, the Boolean Fan Input function block uses a parameter to store the binary coded decimal (BCD) representation of the discrete inputs. The first four discrete inputs are used to construct the BCD ones digit. (Within these first four bits, the first input is the least-significant bit.). The remaining sets of four inputs indicate the BCD tens, hundreds, and thousands digits. When the four bits representing a digit are greater than nine, the digit is limited to nine.
The following figure is an example of Boolean Fan Input function block execution for OUT_INT = 5510. The result is BCD = 1586 and OUT_D = True.
