Device Architecture
Clocking Resources
The Fusion family has a robust collection of clocking peripherals, as shown in the block diagram in
Figure 2-16. These on-chip resources enable the creation, manipulation, and distribution of many
clock signals. The Fusion integrated RC oscillator produces a 100 MHz clock source with no external
components. For systems requiring more precise clock signals, the Actel Fusion family supports an
on-chip crystal oscillator circuit. The integrated PLLs in each Fusion device can use the RC oscillator,
crystal oscillator, or another on-chip clock signal as a source. These PLLs offer a variety of
capabilities to modify the clock source (multiply, divide, synchronize, advance, or delay). Utilizing
the CCC found in the popular Actel ProASIC3 family, Fusion incorporates six CCC blocks. The CCCs
allow access to Fusion global and local clock distribution nets, as described in the "Global Resources
(VersaNets)" section on page 2-10.
Off-Chip On-Chip
100 MHz
RC Oscillator
GNDOSC
VCCOSC
Clock Out to FPGA Core through CCC
XTAL1
GLINT
Crystal Oscillator
XTAL2
To Core
Xtal Clock
PLL/ GLA
NGMUX
CCC
External
Crystal
External
RC
Clock I/Os
GLC
or
CLKOUT
From FPGA Core
Figure 2-16 • Fusion Clocking Options
2-20
Preliminary v1.7
ACTEL [ Actel Corporation ]
