LFEC10E-3F256C Lattice Semiconductor Corp., LFEC10E-3F256C Datasheet - Page 34

• Manufacturer Part Number: LFEC10E-3F256C
• Description: Latticeecp/ec Family of Fpga Devices Has Been Optimized to Deliver Mainstream Fpga Features at Low Cost.for Maximum Performance And Value, The Latticeecp (EConomy Plus) Fpga Concept Combines an Efficient Fpgafabric With High-speed Dedicated Functions
• Manufacturer: Lattice Semiconductor Corp.

Lattice Semiconductor
Tristate Register Block
The tristate register block provides the ability to register tri-state control signals from the core of the device before
they are passed to the sysIO buffers. The block contains a register for SDR operation and an additional latch for
DDR operation. Figure 2-26 shows the diagram of the Tristate Register Block.
In SDR mode, ONEG1 feeds one of the flip-flops that then feeds the output. The flip-flop can be configured a D-
type or latch. In DDR mode, ONEG1 is fed into one register on the positive edge of the clock and OPOS1 is
latched. A multiplexer running off the same clock selects the correct register for feeding to the output (D0).
Figure 2-26. Tristate Register Block
Control Logic Block
The control logic block allows the selection and modification of control signals for use in the PIO block. A clock is
selected from one of the clock signals provided from the general purpose routing and a DQS signal provided from
the programmable DQS pin. The clock can optionally be inverted.
The clock enable and local reset signals are selected from the routing and optionally inverted. The global tristate
signal is passed through this block.
DDR Memory Support
Implementing high performance DDR memory interfaces requires dedicated DDR register structures in the input
(for read operations) and in the output (for write operations). As indicated in the PIO Logic section, the EC devices
provide this capability. In addition to these registers, the EC devices contain two elements to simplify the design of
input structures for read operations: the DQS delay block and polarity control logic.
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.
Routing
From
ONEG1
OPOS1
TD
CLK1
*Latch is transparent when input is low.
/LATCH
D
D
D-Type
LE*
Latch
Q
Q
2-24
0
1
LatticeECP/EC Family Data Sheet
Programmed
Control
OUTDDN
0
1
To sysIO
TO
Buffer
Architecture