R
Virtex™-II Platform FPGAs: Detailed Description
Each block SelectRAM cell is a fully synchronous memory,
as illustrated in Figure 30. The two ports have independent
inputs and outputs and are independently clocked.
Table 15: 18 Kbit Block SelectRAM Port Aspect Ratio
Width
Depth
16,384
8,192
4,096
2,048
1,024
512
Address Bus
ADDR[13:0]
ADDR[12:0]
ADDR[11:0]
ADDR[10:0]
ADDR[9:0]
Data Bus
DATA[0]
Parity Bus
N/A
1
2
18 Kbit Block SelectRAM
DATA[1:0]
DATA[3:0]
DATA[7:0]
DATA[15:0]
DATA[31:0]
N/A
DIA
4
N/A
DIPA
ADDRA
9
Parity[0]
Parity[1:0]
Parity[3:0]
WEA
ENA
18
36
ADDR[8:0]
SSRA
CLKA
DOA
DOPA
Read/Write Operations
The Virtex-II block SelectRAM read operation is fully syn-
chronous. An address is presented, and the read operation
is enabled by control signals WEA and WEB in addition to
ENA or ENB. Then, depending on clock polarity, a rising or
falling clock edge causes the stored data to be loaded into
output registers.
DIB
DIPB
ADDRB
WEB
ENB
SSRB
CLKB
DOB
DOPB
The write operation is also fully synchronous. Data and
address are presented, and the write operation is enabled
by control signals WEA or WEB in addition to ENA or ENB.
Then, again depending on the clock input mode, a rising or
falling clock edge causes the data to be loaded into the
memory cell addressed.
DS031_11_071602
Figure 30: 18 Kbit Block SelectRAM in Dual-Port Mode
Port Aspect Ratios
Table 15 shows the depth and the width aspect ratios for the
18 Kbit block SelectRAM. Virtex-II block SelectRAM also
includes dedicated routing resources to provide an efficient
interface with CLBs, block SelectRAM, and multipliers.
A write operation performs a simultaneous read operation.
Three different options are available, selected by configura-
tion:
1. “WRITE_FIRST”
The “WRITE_FIRST” option is a transparent mode. The
same clock edge that writes the data input (DI) into the
memory also transfers DI into the output registers DO
as shown in Figure 31.
Internal
Memory
DO
Data_in
DI
Data_out = Data_in
CLK
WE
Data_in
Address
New
aa
RAM Contents
Data_out
Old
New
New
DS031_14_102000
Figure 31: WRITE_FIRST Mode
DS031-2 (v3.0) August 1, 2003
Product Specification
www.xilinx.com
1-800-255-7778
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