DP Ram Emulator...

[Ludis Langens]

Eric Aos wrote:
> 
> does anyone have a suggestion for battery backup on this beast??
> I've got the rest of it breadboarded, and working (Pic, IDT Ram chip,
> Max 233...) just trying to put the finishing touches on it.

Check out the Maxim MAX808.  It'll handle the 5V to battery switchover. 
It also manages a ~CS signal so that the DPRAM doesn't get corrupted if
a switchover is needed during a memory write.  Finally, there is an
extra output that can be used to disable the ECM side of the DPRAM.

> An alternate thought was echo all writes to the ram to an eeprom, then
> when the time comes, just rebuild the ram. Would this be a more reliable
> method?

Can you copy from the EEPROM to DPRAM fast enough to let the ECM boot
normally?  Alternately, can the PIC wake up quick enough to at least
stuff a dummy reset vector and a branh to itself into the DPRAM?

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/


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