Architecture
LatticeECP2/M Family Data Sheet
Lattice Semiconductor
Figure 2-34. DQS Input Routing for the Bottom Edge of the Device
PADA "T"
LVDS Pair
PADB "C"
PIO A
PIO B
PIO A
PADA "T"
LVDS Pair
PADB "C"
PIO B
PIO A
PADA "T"
LVDS Pair
PADB "C"
PIO B
PIO A
PADA "T"
LVDS Pair
PADB "C"
PIO B
Assigned
sysIO
Buffer
PIO A
DQS Pin
PADA "T"
DQS
Delay
LVDS Pair
PADB "C"
PIO B
PIO A
PADA "T"
LVDS Pair
PADB "C"
PIO B
PIO A
PIO B
PADA "T"
LVDS Pair
PADB "C"
PADA "T"
LVDS Pair
PADB "C"
PIO A
PIO B
PADA "T"
LVDS Pair
PADB "C"
PIO A
PIO B
DLL Calibrated DQS Delay Block
Source synchronous interfaces generally require the input clock to be adjusted in order to correctly capture data at
the input register. For most interfaces a PLL is used for this adjustment. However, in DDR memories the clock
(referred to as DQS) is not free-running so this approach cannot be used. The DQS Delay block provides the
required clock alignment for DDR memory interfaces.
The DQS signal (selected PIOs only, as shown in Figure 2-35) feeds from the PAD through a DQS delay element to
a dedicated DQS routing resource. The DQS signal also feeds polarity control logic, which controls the polarity of
the clock to the sync registers in the input register blocks. Figure 2-35 and Figure 2-36 show how the DQS transi-
tion signals are routed to the PIOs.
The temperature, voltage and process variations of the DQS delay block are compensated by a set of calibration
(6-bit bus) signals from two dedicated DLLs (DDR_DLL) on opposite sides of the device. Each DLL compensates
DQS delays in its half of the device as shown in Figure 2-35. The DLL loop is compensated for temperature, volt-
age and process variations by the system clock and feedback loop.
2-37
LATTICE [ LATTICE SEMICONDUCTOR ]
