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what is the difference between inferring and instantiating

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samcheetah

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what is the difference between inferring a block RAM and instantiating a block RAM. what i have understood is that instantiating something means that you have to tell the synthesizer that i want such and such thing like a RAMB16 etc. whereas if you declare a reg like

Code:
reg [3:0] abc [3:0];

this is inferring block RAM.

so why are there two ways? and which one is better
 

echo47

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To "instantiate RAM" means to explicitly put a RAMB* library module into your HDL. Refer to your "Libraries Guide" chapter "Design Elements" section "RAMB16_*".

To "infer RAM" means to create an HDL register array that the compiler automatically recognizes as a RAMB* block. Refer to your "XST User Guide" chapter "HDL Coding Techniques" section "RAMs/ROMs".

I prefer inferring everything possible, because that makes my HDL code more portable, and it greatly speeds up behavioral simulation. However, some FPGA features cannot be inferred, so then I must instantiate.
 

    samcheetah

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kumar_eee

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Re: what is the difference between inferring and instantiati

Instantiation:
Instantiation allows one module to incorporate a copy of another module into itself.

Inferring:
Inferring means all the resources are available in the chip itself, in your design u r going to use that resource...
 

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