Ddr Output Registers - Altera Cyclone IV Device Handbook

7–14

DDR Output Registers

A dedicated write DDIO block is implemented in the DDR output and output enable
paths.
Figure 7–8
the I/O element (IOE) registers.
Figure 7–8. Cyclone IV Dedicated Write DDIO
The two DDR output registers are located in the I/O element (IOE) block. Two serial
data streams routed through datain_l and datain_h, are fed into two registers,
output register Ao and output register Bo, respectively, on the same clock edge.
The output from output register Ao is captured on the falling edge of the clock, while
the output from output register Bo is captured on the rising edge of the clock. The
registered outputs are multiplexed by the common clock to drive the DDR output pin
at twice the data rate.
The DDR output enable path has a similar structure to the DDR output path in the
IOE block. The second output enable register provides the write preamble for the DQS
strobe in DDR external memory interfaces. This active-low output enable register
extends the high-impedance state of the pin by half a clock cycle to provide the
external memory's DQS write preamble time specification.
f
For more information about Cyclone IV IOE registers, refer to the
I/O Features
Cyclone IV Device Handbook,
Volume 1
shows how a Cyclone IV dedicated write DDIO block is implemented in
Output Enable
datain_l
datain_h
-90° Shifted Clock
chapter.
Chapter 7: External Memory Interfaces in Cyclone IV Devices
Cyclone IV Devices Memory Interfaces Features
DDR Output Enable Registers
IOE
Register
Output Enable
Register A
OE
data1
data0
IOE
Register
Output Enable
Register B
OE
DDR Output Registers
IOE
Register
data0
Output Register A
O
data1
IOE
Register
®
Output Register B
O
DQ or DQS
Cyclone IV Device
March 2016 Altera Corporation