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LFXP28E6IFTN256I データシート(PDF) 8 Page - Lattice Semiconductor |
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LFXP28E6IFTN256I データシート(HTML) 8 Page - Lattice Semiconductor |
8 / 92 page 2-5 Architecture Lattice Semiconductor LatticeXP2 Family Data Sheet Modes of Operation Each slice has up to four potential modes of operation: Logic, Ripple, RAM and ROM. Logic Mode In this mode, the LUTs in each slice are configured as LUT4s. A LUT4 has 16 possible input combinations. Four- input logic functions are generated by programming the LUT4. Since there are two LUT4s per slice, a LUT5 can be constructed within one slice. Larger LUTs such as LUT6, LUT7 and LUT8, can be constructed by concatenating two or more slices. Note that a LUT8 requires more than four slices. Ripple Mode Ripple mode allows efficient implementation of small arithmetic functions. In ripple mode, the following 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 • Up/Down counter with async clear • Up/Down counter with preload (sync) • Ripple mode multiplier building block • Multiplier support • 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 carry signals, FCI and FCO, are generated per slice in this mode, allowing fast arithmetic functions to be con- structed by concatenating slices. RAM Mode In this mode, a 16x4-bit distributed Single Port RAM (SPR) can be constructed using each LUT block in Slice 0 and Slice 2 as a 16x1-bit memory. Slice 1 is used to provide memory address and control signals. A 16x2-bit Pseudo Dual Port RAM (PDPR) memory is created by using one slice as the read-write port and the other companion slice as the read-only port. 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. For more information on using RAM in LatticeXP2 devices, please see TN1137, LatticeXP2 Memory Usage Guide. Table 2-3. Number of Slices Required For Implementing Distributed RAM ROM Mode ROM mode uses the LUT logic; hence, Slices 0 through 3 can be used in the ROM mode. Preloading is accom- plished through the programming interface during PFU configuration. SPR 16X4 PDPR 16X4 Number of slices 3 3 Note: SPR = Single Port RAM, PDPR = Pseudo Dual Port RAM |
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