Update on 93 Z28 disassembly

[Mike]

>
>I have had some help from several people, thanks everyone.   I am
>going to be updating my web page later tonight (probably late), but
>here is what I have found so far.   I am mostly (with some help)
>decoded the ALDL commands.  My car seems to accept (first bytes) of 
>0xF4, 0x42, 0x40, 0x01, 0x02.   WIth the 0x04 it has several modes
>0x00, 0x01 (basic data out), 0x02, 0x03, 0x04, 0x0a (clear codes).  I

You mean "With the 0xF4..." right?

>have notes on what is in the 0x01 and 0x0a mode, the others are a
>mystery right now.   I have found the data stream for the 0xF4 0x01
>data mode, and I have documentation on what data is contained in that
>mode.   The data it has lines up what what I already determined (at
>the few points I had already determined).  The error for bad prom (two
>different bits) are both setting the bit that should be set in the
>data stream for a bad prom.   Everything that should be accessing a
>A/D port, is, so I know what most of the A/D registers are connected
>to.   I should be able to find out what alot of the code is doing
>since with this info I know what most (or at least 1 or 2 ) of the
>inputs to any formula should b.

It's interesting that this ECM uses an HC11 whose base register set seems
largely intact (compared to "standard" HC11s). Different than any other GM
ECM I've seen, though that number is comparatively limited.

>Here is a question:  I have identified that two of the modes output
>data streams similar to the 0x01 mode (different data, and fewer
>bytes), diacom does not read these data streams at all.  One of the
>data streams has 15 bytes, and the other I believe has 3 bytes.  I
>know from the service manual that there should be info on the ABS
>subsystem and maybe other subsystems available.   Does anyone know
>if all the extra data streams go the same ALDL connector?
>

On these cars (and others with bidirectional ALDL links) the ALDL data is a
shared, one-wire bus between the ECM, the ALDL connector and various other
modules. These can include the CCM (Central Computer Module), the instrument
cluster, climate control, ABS etc. Sometimes some or all of these
peripherals are connected, sometimes none...depends on the option level of
the car.

ALDL diagnostic connector messages, if memory serves, use the F4 identifier.
Other identifiers are reserved for the other modules on the bus. Each
identifier might represent a request from a different device on the bus.
Diacom will only make use of the F4 messages and modes.


-----
 Mike