Eprom Emulation

[steve ravet]

Ludis touched on this previously, here's what he said about read timing:


-------------------
The P4's deselect the PROM for 120ns, but enable it for 360ns.  I don't
how much of the 360 is lost due to data setup time.  OTOH, the C3's
might not deselect the PROM at all between back to back accesses.  Which
brings up the point - it might be good to prevent a bank switch between
data read cycles of a "LDD $89AB".
-------------------

The PIC wasn't nearly fast enough even at 20 MHz to wait for OE to go
away and complete a write before OE came back.  You could probably have
the PIC write the address and data to a flop, then use the deassertion
of OE to create a write signal for the RAM and switch some muxes/buffers
to present the write as soon as the read is done.  Then just put some
NOPs in the code to delay 400 or so ns and you'd be ready for the next
write.  Or a little more hardware to indicate the the write completed. 
Then you wouldn't need the dual port RAM either.

--steve

Eric Aos wrote:
> 
> How frequently does the ECU (730 specifically) read from the EPROM? and
> how long between reads?
> 
> My reason for asking is if I use the Eprom Emulator that can write one
> byte at a time, can I just time my write to happen between reads? like
> maybe pulse the ram write line on the falling edge of the ecu's read?

-- 
Steve Ravet
steve.ravet at arm.com
Advanced Risc Machines, Inc.
www.arm.com