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EP3C120F484C7 Datasheet, PDF (49/274 Pages) Altera Corporation – Cyclone III Device Handbook | |||
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Chapter 3: Memory Blocks in the Cyclone III Device Family
Design Considerations
3â15
Read or Write Clock Mode
Cyclone III device family M9K memory blocks can implement read or write clock
mode for FIFO and simple dual-port memories. In this mode, a write clock controls
the data inputs, write address, and wren registers. Similarly, a read clock controls the
data outputs, read address, and rden registers. M9K memory blocks support
independent clock enables for both the read and write clocks.
When using read or write mode, if you perform a simultaneous read or write to the
same address location, the output read data is unknown. If you require the output
data to be a known value, use either single-clock mode, input clock mode, or output
clock mode and choose the appropriate read-during-write behavior in the
MegaWizard Plug-In Manager.
Single-Clock Mode
Cyclone III device family M9K memory blocks can implement single-clock mode for
FIFO, ROM, true dual-port, simple dual-port, and single-port memories. In this mode,
you can control all registers of the M9K memory block with a single clock together
with clock enable.
Design Considerations
This section describes designing with M9K memory blocks.
Read-During-Write Operations
âSame-Port Read-During-Write Modeâ on page 3â16 and âMixed-Port Read-During-
Write Modeâ on page 3â16 describe the functionality of the various RAM
configurations when reading from an address during a write operation at that same
address.
There are two read-during-write data flows: same-port and mixed-port. Figure 3â14
shows the difference between these flows.
Figure 3â14. Cyclone III Device Family Read-During-Write Data Flow
write_a
Port A
data in
Port B
data in
write_b
read_a
Port A
data out
Port B
data out
Mixed-port
data flow
Same-port
data flow
read_b
December 2011 Altera Corporation
Cyclone III Device Handbook
Volume 1
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