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The counter outputs from the SDRAM PLL can be gated off directly under software control. The divider
values for each clock are set by registers in the clock manager.
Table 2-6: SDRAM PLL Output Assignments
Phase Shift Control
Frequency
Clock Name
Output Counter
PLL
Yes
Up to varies
(1)
ddr_dqs_base_
clk
C0
SDRAM
Yes
Up to
ddr_dqs_
base_clk
x 2
ddr_2x_dqs_
base_clk
C1
Yes
Up to
ddr_dqs_
base_clk
ddr_dq_base_
clk
C2
Yes
osc1_clk
to varies
(1)
h2f_user2_
base_clk
C5
The maximum frequency depends on the speed grade of the
device.
Note:
The following figure shows clock gating for SDRAM PLL clock group. Clock gate blocks in the diagram
indicate clocks which may be gated off under software control. Software is expected to gate these clocks off
prior to changing any PLL or divider settings that might create incorrect behavior on these clocks.
Figure 2-5: SDRAM Clock Group Divide and Gating
h2f_user2_base_clk
Clock Gate
Clock Gate
Clock Gate
Clock Gate
ddr_dqs_base_clk
ddr_2x_dqs_base_clk
ddr_dq_base_clk
ddr_dqs_clk
ddr_2x_dqs_clk
ddr_dq_clk
h2f_user2_clock
C0
C1
C2
C3
C4
C5
SDRAM
PLL
Unused
Unused
The SDRAM PLL output clocks can be phase shifted in real time in increments of 1/8 the VCO frequency.
Maximum number of phase shift increments is 4096.
Altera Corporation
Clock Manager
2-13
SDRAM Clock Group
cv_54002
2013.12.30