Gclk Network Power Down; Clkena Signals - Altera Cyclone IV Device Handbook

5–16
Figure 5–6
the Cyclone IV E device periphery.
Figure 5–6. Clock Control Blocks on Each Side of Cyclone IV E Device
Note to
(1) The left and right sides of the device have two DPCLK pins; the top and bottom of the device have four DPCLK pins.

GCLK Network Power Down

You can disable a Cyclone IV device's GCLK (power down) using both static and
dynamic approaches. In the static approach, configuration bits are set in the
configuration file generated by the Quartus II software, which automatically disables
unused GCLKs. The dynamic clock enable or disable feature allows internal logic to
control clock enable or disable the GCLKs in Cyclone IV devices.
When a clock network is disabled, all the logic fed by the clock network is in an
off-state, thereby reducing the overall power consumption of the device. This function
is independent of the PLL and is applied directly on the clock network, as shown in
Figure 5–1 on page
You can set the input clock sources and the clkena signals for the GCLK multiplexers
through the Quartus II software using the ALTCLKCTRL megafunction.
f
For more information, refer to the

clkena Signals

Cyclone IV devices support clkena signals at the GCLK network level. This allows
you to gate-off the clock even when a PLL is used. Upon re-enabling the output clock,
the PLL does not need a resynchronization or re-lock period because the circuit gates
off the clock at the clock network level. In addition, the PLL can remain locked
independent of the clkena signals because the loop-related counters are not affected.
Cyclone IV Device Handbook,
Volume 1
shows a simplified version of the five clock control blocks on each side of
Clock Input Pins
PLL Outputs
CDPCLK
DPCLK
Internal Logic
Figure 5–6:
5–11.
Chapter 5: Clock Networks and PLLs in Cyclone IV Devices
3 or 4
5
Clock
2 5
Control
Block
2 or 4
5
Five Clock Control
Blocks on Each Side
of the Device
ALTCLKCTRL Megafunction User
Clock Networks
(1)
GCLK
Guide.
October 2012 Altera Corporation