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EP1SGX40D 数据表(PDF) 69 Page - Altera Corporation |
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EP1SGX40D 数据表(HTML) 69 Page - Altera Corporation |
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69 / 262 page  Altera Corporation 69 Preliminary Logic Elements Figure 50. LE in Dynamic Arithmetic Mode Note to Figure 50: (1) The addnsub signal is tied to the carry input for the first LE of a carry chain only. Carry-Select Chain The carry-select chain provides a very fast carry-select function between LEs in arithmetic mode. The carry-select chain uses the redundant carry calculation to increase the speed of carry functions. The LE is configured to calculate outputs for a possible carry-in of 1 and carry-in of 0 in parallel. The carry-in0 and carry-in1 signals from a lower-order bit feed forward into the higher-order bit via the parallel carry chain and feed into both the LUT and the next portion of the carry chain. Carry-select chains can begin in any LE within an LAB. The speed advantage of the carry-select chain is in the parallel pre-computation of carry chains. Because the LAB carry-in selects the precomputed carry chain, not every LE is in the critical path. Only the propagation delay between LAB carry-in generation (LE 5 and LE 10) are now part of the critical path. This feature allows the Stratix GX architecture to implement high-speed counters, adders, multipliers, parity functions, and comparators of arbitrary width. Figure 51 shows the carry-select circuitry in an LAB for a 10-bit full adder. One portion of the LUT generates the sum of two bits using the input signals and the appropriate carry-in bit; the sum is routed to the output of the LE. The register can be bypassed for simple adders or used for data1 LUT data2 data3 addnsub (LAB Wide) clock (LAB Wide) ena (LAB Wide) aclr (LAB Wide) ALD/PRE CLRN D Q ENA ADATA Register chain connection LUT LUT LUT Carry-Out1 Carry-Out0 LAB Carry-In Carry-In0 Carry-In1 (1) sclear (LAB Wide) sload (LAB Wide) LUT chain connection Register chain output Row, column, and direct link routing Row, column, and direct link routing Local routing aload (LAB Wide) Register Feedback |
类似零件编号 - EP1SGX40D |
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类似说明 - EP1SGX40D |
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