Stratix Architecture
Shift Register Support
You can configure embedded memory blocks to implement shift registers
for DSP applications such as pseudo-random number generators, multi-
channel filtering, auto-correlation, and cross-correlation functions. These
and other DSP applications require local data storage, traditionally
implemented with standard flip-flops, which can quickly consume many
logic cells and routing resources for large shift registers. A more efficient
alternative is to use embedded memory as a shift register block, which
saves logic cell and routing resources and provides a more efficient
implementation with the dedicated circuitry.
The size of a w × m × n shift register is determined by the input data
width (w), the length of the taps (m), and the number of taps (n). The size
of a w × m × n shift register must be less than or equal to the maximum
number of memory bits in the respective block: 576 bits for the M512
RAM block and 4,608 bits for the M4K RAM block. The total number of
shift register outputs (number of taps n × width w) must be less than the
maximum data width of the RAM block (18 for M512 blocks, 36 for M4K
blocks). To create larger shift registers, the memory blocks are cascaded
together.
Data is written into each address location at the falling edge of the clock
and read from the address at the rising edge of the clock. The shift register
mode logic automatically controls the positive and negative edge
clocking to shift the data in one clock cycle. Figure 2–14 shows the
TriMatrix memory block in the shift register mode.
Altera Corporation
July 2005
2–25
Stratix Device Handbook, Volume 1
ALTERA [ ALTERA CORPORATION ]
