Chapter 5: Clock Networks and PLLs in the Cyclone III Device Family
5–5
Clock Networks
Figure 5–1 shows the clock control block.
Figure 5–1. Clock Control Block
Clock Control Block
Internal Logic
Enable/
Disable
Global
Clock
DPCLK or CDPCLK
Static Clock Select (3)
Static Clock
Select (3)
C0
C1
CLK[n + 3]
inclk1
inclk0
f
CLK[n + 2]
CLK[n + 1]
CLK[n]
IN
C2
PLL
C3
C4
CLKSWITCH (1)
CLKSELECT[1..0] (2)
Internal Logic (4)
Notes to Figure 5–1:
(1) The clkswitchsignal can either be set through the configuration file or dynamically set when using the manual PLL switchover feature. The
output of the multiplexer is the input clock (fIN) for the PLL.
(2) The clkselect[1..0]signals are fed by internal logic and is used to dynamically select the clock source for the GCLK when the device is in user
mode.
(3) The static clock select signals are set in the configuration file. Therefore, dynamic control when the device is in user mode is not feasible.
(4) You can use internal logic to enable or disable the GCLK in user mode.
Each PLL generates five clock outputs through the c[4..0]counters. Two of these
clocks can drive the GCLK through a clock control block, as shown in Figure 5–1.
f
For more information about how to use the clock control block in the Quartus® II
software, refer to the Clock Control Block (ALTCLKCTRL) Megafunction User Guide.
July 2012 Altera Corporation
Cyclone III Device Handbook
Volume 1
ALTERA [ ALTERA CORPORATION ]
