29.2 Basic Logic Element (BLE)

The Basic Logic Element (BLE) is the primary building block of the CLB module. The BLE contains all of the programmable elements of the CLB. The CLB module contains 32 BLEs.

Figure 29-1. Basic Logic Element (BLE) Simplified Block Diagram
Each BLE contains two main elements (see Figure 29-1):
  • Look-up Table (LUT)
  • Output flop

The LUT is a memory array with four input bits and one output bit. There are sixteen storage elements within the LUT, each corresponding to one logic combination of the four input bits. The four input bits are treated as address inputs to the storage elements within the LUT, selecting one of the elements to be presented as the output. The output can be fed directly to the output of the BLE, or can be routed to the output latch using the BLE Flop Select bit. BLE outputs can be routed to external pins using PPS. The BLE outputs are also internally connected to other peripherals, such as Timer1.

The LUT does not have Reset functionality; however, the output flop can be reset by one of the following actions:
  • Setting the 'CLBMD' Peripheral Module Disable (PMD) bit
  • Device Reset
  • Clearing the EN bit
Important: LUTs that are not used in the application must be configured to all '0' values to minimize current consumption in the design.