RAM 7.0 Betriebsanweisung PDF herunterladen (Seite 31)

DS512 March 1, 2011 www.xilinx.com 31

Product Specification

LogiCORE IP Block Memory Generator v6.1

• Using Byte-Writes. When using byte-writes, memory contents are not corrupted when separate

bytes are written in the same data word. RAM contents are corrupted only when both ports

attempt to Write the same byte. Figure 32 illustrates this case. Assume

ADDRA = ADDRB = 0.

• Synchronous Write-Read Collisions. A synchronous Write-Read collision may occur if a port

attempts to Write a memory location and the other port reads the same location. While memory

contents are not corrupted in Write-Read collisions, the validity of the output data depends on the

Write port operating mode.

• If the Write port is in READ_FIRST mode, the other port can reliably read the old memory

contents.

• If the Write port is in WRITE_FIRST or NO_CHANGE mode, data on the output of the Read

port is invalid.

• In the case of byte-writes, only bytes which are updated will be invalid on the Read port

output.

Figure 33 illustrates Write-Read collisions and the effects of byte-writes.

DOUTB is shown for when port

A is in WRITE_FIRST mode and READ_FIRST mode. Assume

ADDRA = ADDRB = 0, port B is always

reading, and all memory locations are initialized to 0. The RAM contents are never corrupted in Write-

Read collisions.

Collisions and Simple Dual-port RAM

For Simple Dual-port RAM, the operating modes are not selectable, but are automatically set to either

READ_FIRST or WRITE_FIRST depending on the target device family and clocking configuration

(synchronous or asynchronous). The Simple Dual-port RAM is like a true dual-port RAM where only

the Write interface of the A port and the Read interface of B port are connected. The operating modes

X-Ref Target - Figure 32

Figure 32: Write-Write Collision Example

X-Ref Target - Figure 33

Figure 33: Write-Read Collision Example

7777 XX00

WEA[3:0]

DINB[31:0]

RAM Contents

CLKA

b1100

DINA[31:0]

WEB[3:0]

b0011

b0101

b1010

b1110

b0011

b1111

b0110 b1111

7654 3210 BBAA BBAA AAXX XXAA XXXX XXXX

FFFF 3210 BBBB BBBB 0000 0000 BBBB BBBB 2222 2222

7654 FFFF AAAA AAAA 7777 7777 AAAA AAAA 1111 1111

00XX 00XX

WEA[3:0]

DOUTB

AWF

RAM Contents

CLKA

b0000

DINA[31:0]

b0101 b0000 b1100 b1111

3322 00AA

AAAA AAAA 3322 1100 1111 1111

0000 0000

DOUTB

ARF

0000 0000 00AA 00AA

00AA 00AA

00AA

3322 00AA

b0000

1111 1111

1111 111100AA 00AA0000 0000

XXXX XXXX XXXX

1 2 ... 26 27 28 29 30 31 32 33 34 35 36 ... 117 118

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