3800 series II swap, please read :)

[Ludis Langens]

Kevin Margitta wrote:
> 
> Does this mean that the selector code can be
> modified in the prom by changing the 3 bit selector code?

Yes - however, GM does this in an ad hoc manner.  There may or may not
be a PROM location dedicated to specifying the divisor.  Worst case,
program code might have to be patched.

> would the same IC
> be used with a different divisor in the original ecm that I still have...

Yes, that's possible.

> possible IC swap here?

No, the IC is programmed via software.  All you need to do is reprogram
the EPROM.


Terry Kelly wrote:
>
> That is exactly what the ECM has. However, when I change those bytes, the 4k
> and 2k outputs don't seem to change only the ECM view of NMPH.

Bytes?  There are only three bits to select the hardware divisor.  In
the SyTy, these bits are specified by PROM location 0xc0f2 (aka 0x00f2).

> I think it
> affects the IPC stream too for the dashboard. Guess I could try it again. I
> tried it a few times after the swap was first completed.

The selector bits are different than the constants the ECM uses to
convert the VSS into MPH.  The ECM software gets to read the VSS before
the divisor controlled by the three bits.  The output of that divisor
drives only the 2k&4k VSS outputs.

> Anything cosmic in the divisors? (Why those values).

Don't ask me! ;-)  I suspect it has something to do with a gear driven
DC motor vs. a reluctor type VSS pickup and the number of teeth possible
on the reluctor.

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