P4 registers

[Malcolm Robb, LC 0112G]

Ludis is the guru on this sort of stuff.

What you need to do is take a look at the circuit diagrams on his site, and 
compare them with a dissassembly of the code running in that ECU. For 
instance, if a car has a fuel pump relay, look at the circuits to find 
which chip drives the relay. Then look at the code, and see which bit or 
bits of which register is being set. Once you establish that, you can be 
99% certain

This task is relatively easy with discrete inputs and outputs (fans, relays 
& switches), more complex with pulse width modulated outputs (like boost 
solenoids) and very difficult with complex outputs, like spark and fuel 
injectors. Data sheets for the chips you mention would solve all the 
difficulties, but that ain't gonna happen (please someone prove me wrong)

I'm far from certain on this, but I suspect that most of the discrete 
outputs in my car are coming from a PWM capable device. All they do is set 
the duty cycle to either 0% (low/off) or 100% (high/on). Therefore, in one 
application of the ECU a given register might simply be switching something 
on or off, and in another application, the same register may be being used 
in PWM mode.

The 45154 is reasonably well understood by looking at Ludis's circuits. It 
has 8 input pins, and 7 output pins, plus a failsafe timer/counter which is 
used to control the fan, and a VSS multiplexer which is used to select 
between the two types of VSS sensor types. The chip is controlled via a 
serial bus (called the SPI bus) from the main CPU. The CPU can read the 
input pins and write the output pins via the SCI bus.

 My ECU doesn't contain either the 34984 or 988, so I can't say anything 
about them.

Cheers,
Malcolm

-----Original Message-----
From:	Pat Ford [SMTP:pat at istop.com]
Sent:	Wednesday, September 05, 2001 9:39 PM
To:	gmecm
Subject:	P4 registers

Hi All:
 Can anyone point me to info on U13 which is a 16034984 and/or the
16034988 and 16045154.

----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org