Altera Cyclone IV, Device Handbook

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Chapter 7: External Memory Interfaces in Cyclone IV Devices 7–13
Cyclone IV Devices Memory Interfaces Features
March 2016 Altera Corporation Cyclone IV Device Handbook,
Volume 1
Figure 7–7 illustrates Cyclone IV DDR input registers.
These DDR input registers are implemented in the core of devices. The DDR data is
first fed to two registers, input register A
I
and input register B
I
.
■
Input register A
I
captures the DDR data present during the rising edge of the clock
■ Input register B
I
captures the DDR data present during the falling edge of the clock
■ Register C
I
aligns the data before it is synchronized with the system clock
The data from the DDR input register is fed to two registers,
sync_reg_h
and
sync_reg_l
, then the data is typically transferred to a FIFO block to synchronize the
two data streams to the rising edge of the system clock. Because the read-capture
clock is generated by the PLL, the read-data strobe signal (
DQS
or CQ) is not used
during read operation in Cyclone IV devices; hence, postamble is not a concern in this
case.
Figure 7–7. Cyclone IV DDR Input Registers
datao u t_h
LE
Register
LE
Register
LE
Register
DQ
datao u t_l
Inp u t Register B
I
Inp u t Register A
I
neg_reg_o u t
Register C
I
DDR Inp u t Registers in Cyclone IV Device
Capt u re Clock
PLL