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Virtex-II Platform FPGAs: Detailed Description
R
DS031-2 (v3.0) August 1, 2003
Product Specification
1-800-255-7778Module 2 of 4
24
2.
“READ_FIRST”
The “READ_FIRST” option is a read-before-write mode.
The same clock edge that writes data input (DI) into the memory also transfers the prior content of the memory cell
addressed into the data output registers DO, as shown in
Figure 32
.
3.
“NO_CHANGE”
The “NO_CHANGE” option maintains the content of the output registers, regardless of the write operation. The clock edge
during the write mode has no effect on the content of the data output register DO. When the port is configured as
“NO_CHANGE”, only a read operation loads a new value in the output register DO, as shown in
Figure 33
.
Figure 32:
READ_FIRST Mode
CLK
WE
Data_in
Data_in
New
aa
Old
Address
Internal
Memory
DO
Prior stored data
Data_out
DI
DS031_13_102000
RAM Contents
New
Old
Figure 33:
NO_CHANGE Mode
CLK
WE
Data_in
Data_in
New
aa
Last Read Cycle Content (no change)
Address
Internal
Memory
DO
No change during write
Data_out
DI
DS031_12_102000
RAM Contents
New
Old