wide ROM

Hi, I want a ROM in FPGA which is 85 bits wide, is it possible to have one? Thanks

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bxbxb3
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It depends. If you want 16-address depth, you can use 85 LUTs. With Xilinx 18K BlockRAMs, you can get 256x72 bits wide in one BlockRAM. For more, you need two BlockRAMs in parallel. Peter Alfke, Xilinx (from home)

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Peter Alfke

Hi,

Yes. In Altera's devices, you just use the "lpm_rom" megafunction described in

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The LPM_ROM lets you build a ROM of up to 256 bits wide by whatever depth you want; the Quartus II software will auotmatically figure out the best way to implement your ROM in the available memory blocks for the family you are targeting.

For example, if you want to make a 96-bit wide by 32-bit deep ROM, the software might map it into three memory blocks, each 32-bits wide by 32-bits deep.

For very shallow ROMs, you might be better off mapping to logic -- a 4-LUT is just a 16-bit deep by 1-bit wide ROM after all. I don't know the best way to do this (LPM_ROM only targets RAMs, I believe), but please ask if you are interested and I'll ask around to find out.

Regards,

Paul Leventis Altera Corp.

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Paul Leventis (at home)

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