Actel Fusion Mixed-Signal FPGAs
The NGMUX macro is simplified to show the two clock options that have been selected by the
GLMUXCFG[1:0] bits. Figure 2-25 illustrates the NGMUX macro. During design, the two clock
sources are connected to CLK0 and CLK1 and are controlled by GLMUXSEL[1:0] to determine which
signal is to be passed through the MUX.
CLK0
GL
CLK1
GLMUXSEL[1:0]
Figure 2-25 • NGMUX Macro
The sequence of switching between two clock sources (from CLK0 to CLK1) is as follows
(Figure 2-26):
•
•
GLMUXSEL[1:0] transitions to initiate a switch.
GL drives one last complete CLK0 positive pulse (i.e., one rising edge followed by one falling
edge).
•
•
•
From that point, GL stays LOW until the second rising edge of CLK1 occurs.
At the second CLK1 rising edge, GL will begin to continuously deliver the CLK1 signal.
Minimum tsw = 0.05 ns at 25°C (typical conditions)
For examples of NGMUX operation, refer to the Fusion Handbook.
tSW
CLK0
CLK1
GLMUXSEL[1:0]
GL
Figure 2-26 • NGMUX Waveform
Preliminary v1.7
2-33
ACTEL [ Actel Corporation ]
