RAM 8.0 BUX II Series Betriebsanweisung Seite 22

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22 www.xilinx.com 7 Series FPGAs Memory Resources
UG473 (v1.11) November 12, 2014
Chapter 1: Block RAM Resources
enable is not available in the dual-clock FIFO or ECC mode. Byte-wide write enable is
further described in the Additional RAMB18E1 and RAMB36E1 Primitive Design
Considerations section. Figure 1-8 shows the byte-wide write-enable timing diagram for
the RAMB36E1.
When the RAMB36E1 is configured for a 36-bit or 18-bit wide datapath, any port can
restrict writing to specified byte locations within the data word. If configured in
READ_FIRST mode, the DO bus shows the previous content of the whole addressed word.
In WRITE_FIRST mode, DO shows a combination of the newly written enabled byte(s),
and the initial memory contents of the unwritten bytes.
Block RAM Error Correction Code
Both block RAM and FIFO implementations of the 36 Kb block RAM support a 64-bit Error
Correction Code (ECC) implementation. The code is used to detect single and double-bit
errors in block RAM data read out. Single-bit errors are then corrected in the output data.
Power Gating of Unused Block RAMs
7 series devices power down unused/uninstantiated block RAM blocks at an 18Kb
granularity. Power gating is enabled on every 18Kb block that is not instantiated in the
design to save power. Power-gated 18Kb blocks are not initialized during configuration
and cannot be read back through the configuration interface. Unlike previous FPGA
families, a valid bitstream is required for configuration and readback. Blank bitstreams are
Table 1-5: Available Byte-Wide Write Enables
Primitive Maximum Bit Width Number of Byte-Wide Write Enables
RAMB36E1 TDP mode 36 4
RAMB36E1 SDP mode 72 8
RAMB18E1 TDP mode 18 2
RAMB18E1 SDP mode 36 4
X-Ref Target - Figure 1-8
Figure 1-8: Byte-wide Write Operation Waveforms (x36 WRITE_FIRST)
CLK
WE
DI
ADDR
DO
EN
Disabled Read
XXXX 1111 2222
1111 0011
XXXX
aa bb bb cc
0000 MEM(aa) 1111 1122 MEM(cc)
ReadWrite
MEM(bb)=1111
Byte Write
MEM(bb)=1122
UG473_c1_08_052610
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