Chapter 8: External Memory Interfaces in the Cyclone III Device Family
8–13
Cyclone III Device Family Memory Interfaces Features
f
For more information about Cyclone III device family IOE registers, refer to the
I/O Features in the Cyclone III Device Family chapter.
Figure 8–6 shows how the second output enable register extends the DQS
high-impedance state by half a clock cycle during a write operation.
(1)
Figure 8–6. Extending the OE Disable by Half a Clock Cycle for a Write Transaction
System clock
(outclock for DQS)
OE for DQS
Delay
90o
(from logic array)
by Half
a Clock
Cycle
Preamble
Postamble
DQS
Write Clock
(outclock for DQ,
o
-90 phase shifted
from System Clock)
datain_h
(from logic array)
D0
D2
D3
datain_I
(from logic array)
D1
OE for DQ
(from logic array)
DQ
D0
D1
D2
D3
Note to Figure 8–6:
(1) The waveform reflects the software simulation result. The OEsignal is an active low on the device. However, the Quartus II software implements
the signal as an active high and automatically adds an inverter before the AOE register D input.
OCT
Cyclone III device family supports calibrated on-chip series termination (RS OCT) in
both vertical and horizontal I/O banks. To use the calibrated OCT, you must use the
RUP and RDN pins for each RS OCT control block (one for each side). You can use
each OCT calibration block to calibrate one type of termination with the same VCCIO
for that given side.
f
For more information about Cyclone III device family OCT calibration block, refer to
the Cyclone III Device I/O Features chapter.
PLL
When interfacing with external memory, the PLL is used to generate the memory
system clock, the write clock, the capture clock and the logic-core clock. The system
clock generates the DQSwrite signals, commands, and addresses. The write-clock is
shifted by -90° from the system clock and generates the DQsignals during writes. You
can use the PLL reconfiguration feature to calibrate the read-capture phase shift to
balance the setup and hold margins.
July 2012 Altera Corporation
Cyclone III Device Handbook
Volume 1
ALTERA [ ALTERA CORPORATION ]
