R
Virtex™-II Platform FPGAs: Detailed Description
Distributed SelectRAM memory modules are synchronous
(write) resources. The combinatorial read access time is
extremely fast, while the synchronous write simplifies
high-speed designs. A synchronous read can be imple-
mented with a storage element in the same slice. The dis-
tributed SelectRAM memory and the storage element share
the same clock input. A Write Enable (WE) input is active
High, and is driven by the SR input.
FFY
FF
LATCH
DY
YQ
Attribute
D
Q
CE
CK
INIT1
INIT0
SRHIGH
SRLOW
SR REV
Table 8 shows the number of LUTs (2 per slice) occupied by
each distributed SelectRAM configuration.
BY
FFX
Table 8: Distributed SelectRAM Configurations
FF
LATCH
RAM
Number of LUTs
DX
D
XQ
Q
16 x 1S
16 x 1D
32 x 1S
32 x 1D
64 x 1S
64 x 1D
128 x 1S
1
2
2
4
4
8
8
Attribute
CE
CE
CK
SR REV
INIT1
INIT0
SRHIGH
SRLOW
CLK
SR
BX
Reset Type
SYNC
ASYNC
DS031_22_110600
Figure 17: Register / Latch Configuration in a Slice
Notes:
1. S = single-port configuration; D = dual-port configuration
The set and reset functionality of a register or a latch can be
configured as follows:
For single-port configurations, distributed SelectRAM mem-
ory has one address port for synchronous writes and asyn-
chronous reads.
•
•
•
•
•
•
•
No set or reset
Synchronous set
Synchronous reset
Synchronous set and reset
Asynchronous set (preset)
Asynchronous reset (clear)
Asynchronous set and reset (preset and clear)
For dual-port configurations, distributed SelectRAM mem-
ory has one port for synchronous writes and asynchronous
reads and another port for asynchronous reads. The func-
tion generator (LUT) has separated read address inputs
(A1, A2, A3, A4) and write address inputs (WG1/WF1,
WG2/WF2, WG3/WF3, WG4/WF4).
The synchronous reset has precedence over a set, and an
asynchronous clear has precedence over a preset.
In single-port mode, read and write addresses share the
same address bus. In dual-port mode, one function genera-
tor (R/W port) is connected with shared read and write
addresses. The second function generator has the A inputs
(read) connected to the second read-only port address and
the W inputs (write) shared with the first read/write port
address.
Distributed SelectRAM Memory
Each function generator (LUT) can implement a 16 x 1-bit
synchronous RAM resource called a distributed SelectRAM
element. The SelectRAM elements are configurable within
a CLB to implement the following:
•
•
•
•
•
•
•
Single-Port 16 x 8 bit RAM
Single-Port 32 x 4 bit RAM
Single-Port 64 x 2 bit RAM
Single-Port 128 x 1 bit RAM
Dual-Port 16 x 4 bit RAM
Dual-Port 32 x 2 bit RAM
Dual-Port 64 x 1 bit RAM
DS031-2 (v3.0) August 1, 2003
Product Specification
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1-800-255-7778
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