EPM7064B PDF资料下载(10/66 页)Programmable Logic Device

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Altera Corporation

MAX 7000B Programmable Logic Device Data Sheet

Parallel Expanders

Parallel expanders are unused product terms that can be allocated to a

neighboring macrocell to implement fast, complex logic functions.

Parallel expanders allow up to 20 product terms to directly feed the

macrocell

logic, with five product terms provided by the macrocell and

15 parallel expanders provided by neighboring macrocells in the LAB.

The Altera Compiler can automatically allocate up to three sets of up to

five parallel expanders to the macrocells that require additional product

terms. Each set of five parallel expanders incurs a small, incremental

timing delay (

PEXP

). For example, if a macrocell requires 14 product

terms, the Compiler uses the five dedicated product terms within the

macrocell and allocates two sets of parallel expanders; the first set

includes five product terms and the second set includes four product

terms, increasing the total delay by 2

PEXP

Two groups of eight macrocells within each LAB (e.g., macrocells 1

through 8, and 9 through 16) form two chains to lend or borrow parallel

expanders. A macrocell borrows parallel expanders from lower-

numbered macrocells. For example, macrocell 8 can borrow parallel

expanders from macrocell 7, from macrocells 7 and 6, or from macrocells

7, 6, and 5. Within each group of eight, the lowest-numbered macrocell

can only lend parallel expanders and the highest-numbered macrocell can

only borrow them.

Figure 4

shows how parallel expanders can be

borrowed from a neighboring macrocell.

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