Subject: Re: Question on ROM // Your opinion on reply
From: VhdlCohen@aol.com
Date: Sat Jul 13 2002 - 12:44:08 PDT
In a message dated 7/13/02 12:34:19 PM Pacific Daylight Time,
jwill@AstraGate.net writes:
> I think possibly some other way than an
> INITIAL statement should be allowed, but
> the contents of a ROM should be
> fixed before time 0+ and unalterable by the
> simulation.
Section 5.6 shows 3 ways:
5.6 Modeling Read-Only Memories (ROM)
An asynchronous ROM shall be modeled as combinational logic using one of the
following styles:
a) One-dimensional array with data in case statement (see 5.6.1).
b) Two-dimensional array with data in initial statement (see 5.6.2).
c) Two-dimensional array with data in text .le (see 5.6.3).
We did not state in the spec that the contnet of the rom is fixed before time
0+.
We did state that "It is an error to write to such
a memory from any other procedural block other than the initial statement in
which it is initialized."
I suggest we keep what we have on that issue.
>
> The only problem I can foresee is one of
> the design of a PROM programming system.
> In that case, calling the PROM being programmed
> a "rom", but declaring it as a RAM should work.
Is that a function of the attribute?
Name is immaterial, but attributes will select a particular implementation.
I thus understand from you Jim that you approve my proposal of local
variables.
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Ben Cohen Publisher, Trainer, Consultant (310) 721-4830
<A HREF="http://www.vhdlcohen.com/">http://www.vhdlcohen.com/> vhdlcohen@aol.com
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* Component Design by Example ", 2001 isbn 0-9705394-0-1
* VHDL Coding Styles and Methodologies, 2nd Edition, 1999 isbn 0-7923-8474-1
* VHDL Answers to Frequently Asked Questions, 2nd Edition, isbn 0-7923-8115
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