
7 Series FPGAs Memory Resources www.xilinx.com 21
UG473 (v1.11) November 12, 2014
Additional Block RAM Features in 7 Series Devices
Cascadable Block RAM
In the 7 series FPGAs block RAM architecture, two 32K x 1 RAMs can be combined to form
one 64K x 1 RAM without using local interconnect or additional CLB logic resources. Any
two adjacent block RAMs can be cascaded to generate a 64K x 1 block RAM. Increasing the
depth of the block RAM by cascading two block RAMs is available only in the 64K x 1
mode. Further information on cascadable block RAM is described in the Additional
RAMB18E1 and RAMB36E1 Primitive Design Considerations section. For other wider
and/or deeper sizes, consult the Creating Larger RAM Structures section. Figure 1-7
shows the block RAM with the appropriate ports connected in the Cascadable mode.
Byte-Wide Write Enable
The byte-wide write enable feature of the block RAM allows writing eight-bit (one byte)
portions of incoming data. There are four independent byte-wide write enable inputs to
the RAMB36E1 true dual-port RAM. There are eight independent byte-wide write enable
inputs to block RAM in simple dual-port mode (RAMB36E1 in SDP mode). Table 1-5
summarizes the byte-wide write enables for the 36Kb and 18Kb block RAM. Each
byte-wide write enable is associated with one byte of input data and one parity bit. All
byte-wide write enable inputs must be driven in all data width configurations. This feature
is useful when using block RAM to interface with a microprocessor. Byte-wide write
WRCLK Write Data Clock
WREN Write Port Enable
Notes:
1. Block RAM primitive port names can be different from the port function names.
Table 1-4: Simple Dual-Port Functions and Descriptions (Cont’d)
Port Function Description
X-Ref Target - Figure 1-7
Figure 1-7: Cascadable Block RAM
DO
Not Used
DI
DI
CASCADEIN
Connect to logic High or Low
CASCADEOUT
(No Connect)
A[14:0]
WE
DO
A15
A15
A[14:0]
DO
DI
DI
A[14:0]
WE
DO
DQ
DQ
DQ
DQ
DQ
DQ
DQ
DQ
A15
A15
A[14:0]
WE[3:0]
WE[3:0]
Interconnect
Block RAM
RAM_EXTENSION =
UPPER(0)
RAM_EXTENSION =
LOWER(1)
0
1
0
1
0
1
0
1
UG473_c1_07_040411
CASCADEIN of Top
CASCADEOUT of Bottom
Optional
Output FF
Optional
Output FF
Kommentare zu diesen Handbüchern