LAXP2-17E-5FTN256E Lattice, LAXP2-17E-5FTN256E Datasheet - Page 36

• Manufacturer Part Number: LAXP2-17E-5FTN256E
• Description: IC FPGA AUTO 17K LUTS 256-BGA
• Manufacturer: Lattice

Specifications of LAXP2-17E-5FTN256E

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Lattice Semiconductor
Figure 2-31. DQS Local Bus
Polarity Control Logic
In a typical DDR memory interface design, the phase relationship between the incoming delayed DQS strobe and
the internal system clock (during the READ cycle) is unknown. The LA-LatticeXP2 family contains dedicated cir-
cuits to transfer data between these domains. To prevent set-up and hold violations, at the domain transfer between
DQS (delayed) and the system clock, a clock polarity selector is used. This changes the edge on which the data is
registered in the synchronizing registers in the input register block and requires evaluation at the start of each
READ cycle for the correct clock polarity.
Prior to the READ operation in DDR memories, DQS is in tristate (pulled by termination). The DDR memory device
drives DQS low at the start of the preamble state. A dedicated circuit detects this transition. This signal is used to
control the polarity of the clock to the synchronizing registers.
*DQSXFERDEL shifts ECLK1 by 90% and is not associated with a particular PIO.
DQSXFER
DQS
DQS
DCNTL[6:0]
ECLK1
DQSXFER
DCNTL[6:0]
CLK1
GSR
DQS
CEI
2-33
DQSXFERDEL*
Polarity Control
DQSDEL
Logic
PIO
PIO
To DDR
Register Block
Register Block
Reg.
Output
Input
Calibration bus
To Sync
from DLL
LA-LatticeXP2 Family Data Sheet
Reg.
Buffer
Buffer
sysIO
sysIO
DI
DI
Strobe
Datain
DDR
DQS
PAD
PAD
Architecture