RAM 7.0 Betriebsanweisung PDF herunterladen (Seite 30)

LogiCORE IP Block Memory Generator v6.1

30 www.xilinx.com DS512 March 1, 2011

Product Specification

Byte-Write Example

Consider a Single-port RAM with a data width of 24 bits, or 3 bytes with byte size of 8 bits. The Write

enable bus,

WEA, consists of 3 bits. Figure 31 illustrates the use of byte-writes, and shows the contents

of the RAM at address 0. Assume all memory locations are initialized to 0.

Write First Mode Considerations

When performing a Write operation in WRITE_FIRST mode, the concurrent Read operation shows the

newly written data on the output of the core. However, when using the byte-Write feature in Kintex-7,

Virtex-7, Virtex-6, Virtex-5, Virtex-4, Spartan-6, and Spartan-3A/3A DSP devices or the Read-to-Write

aspect ratio feature in Kintex-7, Virtex-7, Virtex-6, Virtex-5 and Virtex-4 devices, the output of the

memory cannot be guaranteed.

Collision Behavior

The Block Memory Generator core supports Dual-port RAM implementations. Each port is equivalent

and independent, yet they access the same memory space. In such an arrangement, is it possible to have

data collisions. The ramifications of this behavior are described for both asynchronous and

synchronous clocks below.

Collisions and Asynchronous Clocks: General Guidelines

Using asynchronous clocks, when one port writes data to a memory location, the other port must not

Read or Write that location for a specified amount of time. This clock-to-clock setup time is defined in

the device data sheet, along with other block RAM switching characteristics.

Collisions and Synchronous Clocks: General Guidelines

Synchronous clocks cause a number of special case collision scenarios, described below.

• Synchronous Write-Write Collisions. A Write-Write collision occurs if both ports attempt to Write

to the same location in memory. The resulting contents of the memory location are unknown. Note

that Write-Write collisions affect memory content, as opposed to Write-Read collisions which only

affect data output.

X-Ref Target - Figure 31

Figure 31: Byte-Write Example

WEA[2:0]

DINA[23:0]

RAM Contents

CLKA

ADDRA[15:0]

b011

FF EE DD

0000

CC BB AA 33 22 11 00 FF 0099 88 77 66 55 44

b010 b101 b000 b110 b010

00 EE DD 00 BB DD 33 22 77 33 FF 7799 BB 77

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RAM 7.0 Betriebsanweisung Seite 30