DQS Logic Block
Each DQS/CQ/CQn/QK# pin is connected to a separate DQS logic block, which consists of the update enable
circuitry, DQS delay chains, and DQS postamble circuitry.
The following figure shows the DQS logic block.
Figure 6-13: DQS Logic Block in Cyclone V Devices
Update
Enable
Circuitry
7
7
7
7
dqsin
delayctrlin [6:0]
dqsupdateen
DQS Delay Chain
Bypass
7
dqsbusout
1
0
0
1
1
0
Input Reference
Clock
Postamble
Enable
dqsenablein
zerophaseclk
(Postamble clock)
dqsenableout
levelingclk
(Read-leveled postamble clock)
DQS Enable Control Circuit
DQS Pin
DQS Enable
dqsin
D
Q
PRE
0
1
dqsenable
D
Q
D
Q
D
Q
D
Q
DQS Postamble Circuitry
D Q
7
7
DQS
del
ay
settings
from
the
DLL
delayctrlin [6:0]
2
DQS
del
ay
settings
from
the
DLL
Core
Logic
7
<dqs delay chain bypass>
enaphasetransferreg
0
1
2
<delay dqs enable>
dqsdisablen
This clock can come from a PLL
output clock or an input clock pin
Applicable only if the DQS
delay settings come from a
side with two DLLs
The dqsenable
signal can also
come from the
FPGA fabric
Update Enable Circuitry
The update enable circuitry enables the registers to allow enough time for the DQS delay settings to travel
from the DQS phase-shift circuitry or core logic to all the DQS logic blocks before the next change.
Both the DQS delay settings and the phase-offset settings pass through a register before going into the DQS
delay chains. The registers are controlled by the update enable circuitry to allow enough time for any changes
in the DQS delay setting bits to arrive at all the delay elements, which allows them to be adjusted at the same
time.
The circuitry uses the input reference clock or a user clock from the core to generate the update enable
output. The UniPHY intellectual property (IP) uses this circuit by default.
Figure 6-14: DQS Update Enable Waveform
This figure shows an example waveform of the update enable circuitry output.
Update Enable
Circuitry Output
System Clock
DQS Delay Settings
Updated every 8 cycles
DLL Counter Update
(Every 8 cycles)
7 bit
DLL Counter Update
(Every 8 cycles)
External Memory Interfaces in Cyclone V Devices
Altera Corporation
CV-52006
DQS Logic Block
6-24
2014.01.10