EPROM Emulator Proposal

[thergen at svn.net]

Battery backed rams I've used have usually been very picky about the
states of chip selects during power-up/power-down/power-off.  It's very
easy to do an accidental write to an arbitrary location.  Often, chip
selects and write enables are active low.  Low is where all the signals go
during power-down (hence the need for the special handling of chip
select).  Chip select level(s) during power off may also determine whether
or not the lowest power state is entered which can severly affect backup
battery life.

Tom

On Wed, 7 Apr 1999, Squash wrote:

> But if dpram is battery backed, there should be no
> need for a weird circuit on power-up, right?  It would
> act just like an eeprom?
> 
> Andy
> 
> --- thergen at svn.net wrote:
> > I think it's a good proposal.  I'd like to suggest
> > that a pushbutton
> > switch be part of the design that can be used to
> > reload the default dpram
> > bank from the eprom (assuming it's present) so that
> > you can recover from a
> > corrupted ram image without using a laptop computer.
> >  Power-up/power-down
> > need special attention (as you already know) to
> > avoid corrupting the ram. 
> > Maxim (www.maxim-ic.com) and others make parts with
> > voltage supervisors
> > specifically for memory protection (let me know if
> > you want specifics). 
> >  
> > Tom
> >  
> > On Wed, 7 Apr 1999, Ludis Langens wrote:
> >  
> > > The EPROM emulator debate on this list seems to be
> > going in circles.
> > > Either people have short memories, or there are a
> > lot of new members who
> > > missed the discussion and decisions made in the
> > first few weeks of
> > > gmecm.  Either way, please read through the
> > archives.
> > >
> > > Anyway, here is an emulator proposal based on the
> > prior discussion.  I 
> > > did some ruthless cutting of features and
> > expandability (indicated with
> > > a *).  I propose the use of a single dual-port
> > SRAM (from Cypress or  
> > > IDT) and a 40/44 pin PIC microcontroller to load
> > this RAM.  A battery 
> > > back up will keep the SRAM alive.  This allows an
> > ECM to boot from the
> > > DPRAM immediately upon power-up.  The whole
> > emulator circuit board  
> > > should be small enough to fit inside a
> > '165/'727/'730/'749/'808 ECM.
> > ....
> > 
> > 
> > 
> > 
> 
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