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LFECP1E-3F256I Arkusz danych(PDF) 8 Page - Lattice Semiconductor |
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LFECP1E-3F256I Arkusz danych(HTML) 8 Page - Lattice Semiconductor |
8 / 117 page 2-5 Architecture Lattice Semiconductor LatticeECP/EC Family Data Sheet Modes of Operation Each Slice is capable of four modes of operation: Logic, Ripple, RAM and ROM. The Slice in the PFF is capable of all modes except RAM. Table 2-2 lists the modes and the capability of the Slice blocks. Table 2-2. Slice Modes Logic Mode: In this mode, the LUTs in each Slice are configured as 4-input combinatorial lookup tables. A LUT4 can have 16 possible input combinations. Any logic function with four inputs can be generated by programming this lookup table. Since there are two LUT4s per Slice, a LUT5 can be constructed within one Slice. Larger lookup tables such as LUT6, LUT7 and LUT8 can be constructed by concatenating other Slices. Ripple Mode: Ripple mode allows the efficient implementation of small arithmetic functions. In ripple mode, the fol- lowing functions can be implemented by each Slice: • Addition 2-bit • Subtraction 2-bit • Add/Subtract 2-bit using dynamic control • Up counter 2-bit •Down counter 2-bit • Ripple mode multiplier building block • Comparator functions of A and B inputs -A greater-than-or-equal-to B -A not-equal-to B -A less-than-or-equal-to B Two additional signals: Carry Generate and Carry Propagate are generated per Slice in this mode, allowing fast arithmetic functions to be constructed by concatenating Slices. RAM Mode: In this mode, distributed RAM can be constructed using each LUT block as a 16x1-bit memory. Through the combination of LUTs and Slices, a variety of different memories can be constructed. The Lattice design tools support the creation of a variety of different size memories. Where appropriate, the soft- ware will construct these using distributed memory primitives that represent the capabilities of the PFU. Table 2-3 shows the number of Slices required to implement different distributed RAM primitives. Figure 2-5 shows the dis- tributed memory primitive block diagrams. Dual port memories involve the pairing of two Slices, one Slice functions as the read-write port. The other companion Slice supports the read-only port. For more information on using RAM in LatticeECP/EC devices, please see details of additional technical documentation at the end of this data sheet. Table 2-3. Number of Slices Required For Implementing Distributed RAM Logic Ripple RAM ROM PFU Slice LUT 4x2 or LUT 5x1 2-bit Arithmetic Unit SPR16x2 ROM16x1 x 2 PFF Slice LUT 4x2 or LUT 5x1 2-bit Arithmetic Unit N/A ROM16x1 x 2 SPR16x2 DPR16x2 Number of slices 1 2 Note: SPR = Single Port RAM, DPR = Dual Port RAM |
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