MAX 3000A Programmable Logic Device Family Data Sheet
The Altera development system 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 (tPEXP). 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 × tPEXP
.
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.
Figure 4. MAX 3000A Parallel Expanders
Unused product terms in a macrocell can be allocated to a neighboring macrocell.
From
Previous
Macrocell
Preset
Product-
er
Select
Matrix
Macrocell
Product-
Term Logic
Clock
Clear
Preset
Product-
Term
Select
Matrix
Macrocell
Product-
Term Logic
Clock
Clear
To Next
Macrocell
36 Signals 16 Shared
from PIA
Expanders
Altera Corporation
9
ETC [ ETC ]
