EPM3256A ALTERA [Altera Corporation], EPM3256A Datasheet - Page 9

• Manufacturer Part Number: EPM3256A
• Description: Programmable Logic Device Family
• Manufacturer: ALTERA [Altera Corporation]

Altera Corporation
Figure 4. MAX 3000A Parallel Expanders
Unused product terms in a macrocell can be allocated to a neighboring macrocell.
36 Signals
from PIA
Expanders
16 Shared
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 (t
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 t
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.
borrowed from a neighboring macrocell.
Product-
Product-
Select
Matrix
Select
Matrix
Ter
T T m
MAX 3000A Programmable Logic Device Family Data Sheet
er
Figure 4
Macrocell
Previous
From
shows how parallel expanders can be
PEXP
). For example, if a macrocell
Macrocell
To Next
Preset
Clock
Clear
Preset
Clock
Clear
PEXP
.
Macrocell
Product-
Term Logic
Macrocell
Product-
Term Logic
9