Instantiating RAM & ROM Functions in Verilog HDL

The MAX+PLUS^® II/Synopsys interface offers full support for the memory capabilities of the FLEX^® 10K device family, including synchronous and asynchronous RAM and ROM, cycle-shared dual port RAM, dual-port RAM, single-Clock FIFO, and dual-clock FIFO functions. Altera recommends using the LPM functions lpm_ram_dq, lpm_ram_io, and lpm_rom to instantiate synchronous and asynchronous RAM and ROM. However, if you wish to enter cycle-shared dual port ram (csdpram), dual-port RAM (altdpram), single-Clock FIFO (scfifo), and dual-clock FIFO (dcfifo) functions, or if you wish create simulation models for any supported RAM or ROM function, you can use the Altera-provided genmem utility. Designs that instantiate genmem-generated synchronous and asynchronous RAM and ROM -- such as those used with FPGA Compiler or Design Compiler -- are supported for backward compatibility. Type genmem at the DOS or UNIX prompt to display information on how to use this utility, as well as a list of the functions you can generate.

To instantiate an lpm_ram_dq, lpm_ram_io, or lpm_rom function:

Follow the guidelines in Instantiating LPM Functions in Verilog HDL.

To instantiate other RAM and ROM functions in Verilog HDL, follow these steps:

1. Use the genmem utility to generate a memory model by typing the following command at a DOS or UNIX prompt:

   genmem <memory type> <memory size> -verilog

   For example: genmem scfifo 16x8 -verilog

2. Create a Verilog HDL design that instantiates the <memory name>.v function. The genmem utility produces files with descriptive names that typically include both the memory type and the memory size (e.g., scfifo_16x8_d.v).

   In MAX+PLUS II version 8.3 and lower, running genmem on a PC always creates files named as genmem.vhd, genmem.cmp, and genmem.v, regardless of the memory type and memory size values you specify.

3. (Optional for RAM functions) Specify an initial memory content file:

   • For ROM functions, you must specify the filename of an initial memory content file in the Intel hexadecimal format (.hex) or the Altera^® Memory Initialization File (.mif) format in the Parameter Statement, using the LPM_FILE parameter. The filename must be the same as the instance name; e.g., the u1 instance name must be unique throughout the whole project, and must contain only valid Verilog HDL name characters. The initialization file must reside in the directory containing the project's design files.

   • For RAM functions, specifying a memory initialization file is optional. If you want to use it, you must specify it in the Parameter Statement as described above.

The MIF format is supported only for specifying initial memory content when compiling designs within MAX+PLUS II software. You cannot use an MIF to perform simulation with Synopsys tools prior to MAX+PLUS II compilation. If you use an Intel hexadecimal format file and wish to simulate the file with the VHDL System Simulator Software (VSS) after MAX+PLUS II compilation, you should use the Synopsys intelhex utility to translate the Intel hexadecimal fomat file into a VSS-compatible Synopsys memory file. Refer to the Synopsys VHDL System Simulator Software Tool manual for details about using the intelhex utility.

4. Continue with the steps necessary to complete your Verilog HDL design, as described in Creating Verilog HDL Designs for Use with MAX+PLUS II Software.

Related Links:

• Go to FLEX 10K Devices, which is available on the web, for additional information.

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