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EP1C20F400C7ES 数据表(PDF) 13 Page - Altera Corporation |
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EP1C20F400C7ES 数据表(HTML) 13 Page - Altera Corporation |
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13 / 106 page  Altera Corporation 2–7 May 2008 Preliminary Logic Elements functions. Another special packing mode allows the register output to feed back into the LUT of the same LE so that the register is packed with its own fan-out LUT. This provides another mechanism for improved fitting. The LE can also drive out registered and unregistered versions of the LUT output. LUT Chain and Register Chain In addition to the three general routing outputs, the LEs within a LAB have LUT chain and register chain outputs. LUT chain connections allow LUTs within the same LAB to cascade together for wide input functions. Register chain outputs allow registers within the same LAB to cascade together. The register chain output allows a LAB to use LUTs for a single combinatorial function and the registers to be used for an unrelated shift register implementation. These resources speed up connections between LABs while saving local interconnect resources. “MultiTrack Interconnect” on page 2–12 for more information on LUT chain and register chain connections. addnsub Signal The LE's dynamic adder/subtractor feature saves logic resources by using one set of LEs to implement both an adder and a subtractor. This feature is controlled by the LAB-wide control signal addnsub. The addnsub signal sets the LAB to perform either A + B or A −B. The LUT computes addition; subtraction is computed by adding the two's complement of the intended subtractor. The LAB-wide signal converts to two's complement by inverting the B bits within the LAB and setting carry-in = 1 to add one to the least significant bit (LSB). The LSB of an adder/subtractor must be placed in the first LE of the LAB, where the LAB-wide addnsub signal automatically sets the carry-in to 1. The Quartus II Compiler automatically places and uses the adder/subtractor feature when using adder/subtractor parameterized functions. LE Operating Modes The Cyclone LE can operate in one of the following modes: ■ Normal mode ■ Dynamic arithmetic mode Each mode uses LE resources differently. In each mode, eight available inputs to the LE ⎯the four data inputs from the LAB local interconnect, carry-in0 and carry-in1 from the previous LE, the LAB carry-in from the previous carry-chain LAB, and the register chain connection ⎯are directed to different destinations to implement the desired logic function. LAB-wide signals provide clock, asynchronous clear, asynchronous |
类似零件编号 - EP1C20F400C7ES |
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类似说明 - EP1C20F400C7ES |
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