747 Rom Emulator / design

[thergen at svn.net]

On Thu, 27 Jul 2000, steve ravet wrote:

> 
> As far as DP ram, IDT makes them and they're really no more complicated
> than SRAM.  There are two address busses, two data busses, one of each
> to the EPROM socket and PIC.  As I recall there weren't any contention
> issues to worry about as far as accessing the same address from both
> ports since th ECM only reads, never writes.  go to IDTs WWW page and
> search for IDT7008
> 

Usually, you can't reliably read and write the same address at the same
time on dual port rams.  The 7008 has a "busy" signal for address
collisions.  With additional external logic, it could be guaranteed that
the ecm is always able to read a valid byte.  

Note that it can get interesting when updating a two byte value if the ECM
gets half of the old value and half of the new value.

HTH,
Tom

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