
7 Series FPGAs Memory Resources www.xilinx.com 19
UG473 (v1.11) November 12, 2014
Additional Block RAM Features in 7 Series Devices
• When one port performs a write operation, the other port must not write into the
same location, unless both ports write identical data.
• When one port performs a write operation, the write operation succeeds; the other
port can reliably read data from the same location if the write port is in READ_FIRST
mode. DATA_OUT on both ports then reflects the previously stored data.
If the write port is in either WRITE_FIRST or in NO_CHANGE mode, then the
DATA_OUT on the read port would become invalid (unreliable). The mode setting of
the read-port does not affect this operation.
Additional Block RAM Features in 7 Series Devices
Optional Output Registers
The optional output registers improve design performance by eliminating routing delay to
the CLB flip-flops for pipelined operation. An independent clock and clock enable input is
provided for these output registers. As a result the output data registers hold the value
independent of the input register operation. Figure 1-5 shows the optional output register.
Independent Read and Write Port Width Selection
Each block RAM port has control over data width and address depth (aspect ratio). The
true dual-port block RAM in 7 series FPGAs extends this flexibility to Read and Write
where each individual port can be configured with different data bit widths. For example,
port A can have a 36-bit Read width and a 9-bit Write width, and port B can have an 18-bit
Read width and a 36-bit Write width. See Block RAM Attributes, page 31.
If the Read port width differs from the Write port width, and is configured in
WRITE_FIRST mode, then DO shows valid new data for all the enabled write bytes. The
DO port outputs the original data stored in memory for all not enabled bytes.
Independent Read and Write port width selection increases the efficiency of implementing
a content addressable memory (CAM) in block RAM. This option is available for all
7 series FPGAs true dual-port RAM port sizes and modes.
X-Ref Target - Figure 1-5
Figure 1-5: Block RAM Logic Diagram (One Port Shown)
Register
Optional
Inverter
Latches
Register
Address
DI
WE
EN
CLK
Write
Strobe
Read
Strobe
QDQD
DO
Control Engine
Configurable Options
UG473_c1_05_052610
Memory
Array
(common to
both ports)
Latch
Enable
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