PLUS
ProASIC
Flash Family FPGAs
enable the user to define a wide range of frequency
multipliers and divisors. The clock conditioning circuit can
advance or delay the clock up to 8 ns (in increments of
0.25 ns) relative to the positive edge of the incoming
reference clock. The system also allows for the selection of
output frequency clock phases of 0°, 90°, 180°, and 270°.
signals relative to other signals to assist in the control of
input set-up times. Not all possible combinations of input
and output modes can be used. The degrees of freedom
available in the bidirectional global pad system and in
the clock conditioning circuit have been restricted. This
avoids unnecessary and unwieldy design kit and software
work.
Prior to the application of signals to the rib drivers, they
pass through programmable delay units, one per global
network. These units permit the delaying of global
V
AVDD AGND
GND
DD
GLA
GLB
Global MUX B OUT
Input Pins to the PLL
See Figure 1-15
Clock Conditioning
Circuitry
(Top level view)
External Feedback Signal
Global MUX A OUT
27
Flash
Configuration Bits
Dynamic
+
on page 1-14
4
-
Configuration Bits
8
Clock Conditioning Circuitry Detailed Block Diagram
CLK
Bypass Primary
OBMUX[2:0]
1
P+
P-
FIVDIV[4:0]
DLYB[1:0]
Delay Line 0.0 ns, 0.25 ns,
0.50 ns and 4.00 ns
7
6
5
4
270˚
180˚
90˚
0˚
0
÷n
GLB
PLL Core
÷u
÷m
OBDIV[1:0]
FBDIV[5:0]
2
Clock from Core
(GLINT mode)
1
2
Delay Line
0.25 ns to
4.00 ns,
16 steps,
0.25 ns
increments
0
3
Deskew
Delay
2.95 ns
1
OADIV[1:0]
3
DLYA[1:0]
Delay Line 0.0 ns, 0.25 ns,
0.50 ns and 4.00 ns
XDLYSEL
2
1
÷v
EXTFB
FBDLY[3:0]
GLA
FBSEL[1:0]
OAMUX[1:0]
CLKA
Bypass Secondary
Clock from Core
(GLINT mode)
Notes:
1. FBDLY is a programmable delay line from 0 to 4 ns in 250 ps increments.
2. DLYA and DLYB are programmable delay lines, each with selectable values 0 ps, 250 ps, 500 ps, and 4 ns.
3. OBDIV will also divide the phase-shift since it takes place after the PLL Core.
Figure 1-14 • PLL Block – Top-Level View and Detailed PLL Block Diagram
1-14
v5.2
ACTEL [ Actel Corporation ]
