[Diy_efi] Continuing the chip switcher "problem"

[Robert W Hughes]

1. Check ground connections between scope and ecm carefully
2. More importantly, if the time scale is 5us/div on your plot and this 
is the best your DSO can do, don't use it, it is not good enough for 
anything more than audio.
3. In any case, if there is a changing signal on /OE use the rising edge 
of this to clock your upper address lines into a register like a 374, 
not a 373. This will cause the address lines to affected memory to only 
change when the memory is not being used. If all program code in the 
multiple images is the same and only tabular data is different this 
should make the switching transparent to the cpu.

> More info -  The Not OE line of the eeprom is connected to the not psen
> line at pin 23 of the MCU.  Now further looking at this line, there is a
> 10kohm resistor attached between this line and pin 63 of the mcu which is
> the Vref line.  Pulling it to Vref.
> 
> Not(Psen) - Program Strobe Enable : The strobe pulse to fetch to external
> program memory.
> 
> I'm guessing this is the reason the signal looks so strange.  I'm going to
> take a look at the signal tomorrow when I can plug it back in the car. 
> I'll take some readings right at the MCU.


-- 
Robert W. Hughes (Bob)
BackYard Engineering
29:40.237N, 95:28.726W or perhaps 30:55.265N, 95:20.590W
Houston, Texas "The city with too much Oxygen"
rwhughe at oplink.net

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