EP3SE50F780I3N Altera, EP3SE50F780I3N Datasheet - Page 301

• Manufacturer Part Number: EP3SE50F780I3N
• Description: Stratix III
• Manufacturer: Altera

Altera Corporation
November 2007
f
Phase Offset Control
Each DLL has two phase-offset modules and can provide two separate
DQS delay settings with independent offset, one for the top/bottom I/O
bank and one for the left/right I/O bank, so you can fine-tune the DQS
phase shift settings between two different sides of the device. Even
though you have independent phase offset control, the frequency of the
interface using the same DLL has to be the same. You should use the
phase offset control module for making small shifts to the input signal
and use the DQS phase-shift circuitry for larger signal shifts. For example,
if the DLL only offers a multiple of 30° phase shift, but your interface
needs a 67.5° phase shift on the DQS signal, you can use two delay chains
in the DQS logic blocks to give you 60° phase shift and use the phase
offset control feature to implement the extra 7.5° phase shift.
You can either use a static phase offset or a dynamic phase offset to
implement the additional phase shift. The available additional phase shift
is implemented in 2’s-complement in Gray-code between settings –64
to +63 for frequency mode 0, 1, and 2, and between settings –32 to +31 for
frequency modes 3, 4, and 5. The DQS phase shift is the sum of the DLL
delay settings and the user selected phase offset settings which maxes out
at setting 64 for mode frequency mode 0, 1, and 2, and maxes out at
setting 32 for frequency modes 3, 4, and 5, so the actual physical offset
setting range will be 64 or 32 subtracted by the DQS delay settings from
the DLL.
1
For example, if the DLL determines that DQS delay settings of 28 is
needed to achieve a 30
subtract up to 28 phase offset settings and you can add up to 35 phase
offset settings to achieve the optimal delay that you need. However, if the
same DQS delay settings of 28 is needed to achieve 30
frequency mode 4, you can still subtract up to 28 phase offset settings, but
you can only add up to 3 phase offset settings before the DQS delay
settings reach their maximum settings, because DLL frequency mode 4
only uses 5-bit DLL delay settings.
Refer to the
in volume 2 of the Stratix III Device Handbook for information on the
value for each step.
When using this feature, you need to monitor the DQS delay
settings to know how many offsets you can add and subtract in
the system. Note that the DQS delay settings output by the DLL
are also Gray-coded.
DC and Switching Characteristics of Stratix III Devices
o
phase shift in DLL frequency mode 1, you can
External Memory Interfaces in Stratix III Devices
Stratix III Device Handbook, Volume 1
o
phase shift in DLL
chapter
8–31