EP2AGX95EF29C6N Datasheet, PDF (236/380 Pages) Altera Corporation – Device Interfaces and Integration

7–34
Chapter 7: External Memory Interfaces in Arria II Devices
Arria II External Memory Interface Features
DQS Logic Block
Each DQS/CQ and CQn pin is connected to a separate DQS logic block, which
consists of DQS delay chains, update enable circuitry, and DQS postamble circuitry
(refer to Figure 7–21).
Figure 7–21. DQS Logic Block for Arria II Devices
DQS Enable
dqsenable (2)
DQS Delay Chain
PRE
QD
Bypass
DQS/CQ or
CQn Pin
dqsin
dqsin
<phase_setting>
dqsbusout
DQS bus
6
0
6
1
6
offsetctrlin [5:0]
6
Phase offset
6
settings from
0
DQS phase-shift
DQ
1
D
circuitry
DQS delay
settings from the
DQS phase-shift
circuitry
<dqs_offsetctrl_enable>
6
delayctrlin [5:0]
Input Reference
Clock (1)
6
0
1
6
<dqs_ctrl_latches_enable>
Q
dqsupdateen
Update
Enable
Circuitry
Postamble
Enable
Resynchronization
Clock
DQS Enable Control
dqsenablein
DQ
clk
0 dqsenableout
1
DQ
<delay_dqs_enable_by_half_cycle>
Notes to Figure 7–21:
(1) The input reference clock for the DQS phase-shift circuitry can come from a PLL output clock or an input clock pin. For the exact PLL and input
clock pin, refer to Table 7–6 on page 7–28 and Table 7–10 on page 7–32.
(2) The dqsenable signal can also come from the Arria II GX FPGA fabric.
DQS Delay Chains
DQS delay chains consist of a set of variable delay elements to allow the DQS/CQ and
CQn in out signals to be shifted by the amount specified by the DQS phase-shift
circuitry or the logic array. There are four delay elements in the DQS delay chain; the
first delay chain closest to the DQS/CQ or CQn pin can either be shifted by the DQS
delay settings or by the sum of DQS delay setting and the phase-offset setting. The
number of delay chains required is transparent because the ALTMEMPHY
megafunction and UniPHY IP core automatically set it when you choose the
operating frequency. The DQS delay settings can come from the DQS phase-shift
circuitry on either end of the I/O banks or from the logic array.
Arria II Device Handbook Volume 1: Device Interfaces and Integration
June 2011 Altera Corporation