SX-A Family FPGAs
Logic Module Design
The SX-A family architecture is described as a “sea-of-
modules” architecture because the entire floor of the
device is covered with a grid of logic modules with
virtually no chip area lost to interconnect elements or
routing. The Actel SX-A family provides two types of
logic modules: the register cell (R-cell) and the
combinatorial cell (C-cell).
The R-cell contains a flip-flop featuring asynchronous clear,
asynchronous preset, and clock enable, using the S0 and S1
lines control signals (Figure
The R-cell registers feature
programmable clock polarity selectable on a register-by-
register basis. This provides additional flexibility while
allowing mapping of synthesized functions into the SX-A
FPGA. The clock source for the R-cell can be chosen from
either the hardwired clock, the routed clocks, or internal
logic.
The C-cell implements a range of combinatorial functions
of up to five inputs (Figure
Inclusion of the DB input
and its associated inverter function allows up to 4,000
different combinatorial functions to be implemented in a
single module. An example of the flexibility enabled by
the inversion capability is the ability to integrate a 3-input
exclusive-OR function into a single C-cell. This facilitates
construction of 9-bit parity-tree functions with 1.9 ns
propagation delays.
Module Organization
All C-cell and R-cell logic modules are arranged into
horizontal banks called Clusters. There are two types of
Clusters: Type 1 contains two C-cells and one R-cell, while
Type 2 contains one C-cell and two R-cells.
Clusters are grouped together into SuperClusters
SuperCluster 1 is a two-wide
grouping of Type 1 Clusters. SuperCluster 2 is a two-wide
group containing one Type 1 Cluster and one Type 2
Cluster. SX-A devices feature more SuperCluster 1
modules than SuperCluster 2 modules because designers
typically require significantly more combinatorial logic
than flip-flops.
S0
Routed
Data Input S1
PRE
DirectConnect
Input
D Q
Y
HCLK
CLKA,
CLKB,
Internal Logic
Figure 1-2 •
R-Cell
CLR
CKS
CKP
D0
D1
Y
D2
D3
Sa
Sb
DB
A0 B0
Figure 1-3 •
C-Cell
A1 B1
1 -2
v5.3
ACTEL [ Actel Corporation ]
