165 $6e 6E Expanded XDF file

What is the SAM cell? There are also SAM cell A & B, SAM filter etc. Haven't seen this in other XDFs or maybe it is called something else.

Also the PID term. Closed loop PID for X seconds etc.

Any thoughts?

 

SAM= stay alive memory

 

Thank you. So what does this do or where can I find out more about it?

 

It is just memory (RAM) that stays alive when the key is off. From $00 to $2F. It is powered via the battery lead to the ECM, so unless the battery is disconnected the contents are retained. Used for the BLM cells, stored malfunction codes, some IAC parameters, and mask dependent some other odds & ends.

When "SAM" is used in context of BLM cells, $6E and $8D retain the values of two cells using a different method. Two of the sixteen cells are stored in a separate location. The values in those locations are changed slowly over time via filtering, and only when the engine temperature is within a certain range (I'm looking at $8D).

At key-on those two cells are limit checked and restored into the BLM matrix. The other 14 cells are limit checked via a different set of limits.

RBob.

 

P4 chipset memory map

Memory location Purpose
0x0000-0x00ff Battery backed static ram
0x0100-0x01ff Non-battery backed static ram, cleared when the key is off
0x0200-0x03ff On chip SRAM in enhanced P4 MPUs
0x0400-0x04ff GM debugging HUD ram variables (if present)
0x3dc0-0x3dff Extra timer chip
0x3f80-0x3fbf Extra timer chip
0x3fc0-0x3fff P4 timer chip
0x4000-0x400f memory mapped I/O registers
0x5000-0x5fff GM debugging HUD hardware
0x5800-0x58ff GM debugging HUD code
0x6000-0x6fff GM debugging HUD code
0xc000-0xffff EPROM (27128, 16K EPROM, code and data)
0x8000-0xffff EPROM (27256, 32K EPROM, code and data)
0xfff0-0xfffe interrupt vectors

 

Aah I see. So this is how it "remembers" the data. Ok, then would this data be why when I update a bin, after the next restart it takes a while for everything to settle down? For example, let's say at idle blms are 132, make a change and on restart, at first, I will be real rich but after a little time the blm's come down and the afr is back to where it was before. IOW the motor/tune has to run for a while before the changes seem to take affect.

 

Yes, which is why when tuning it is best to set the key-on BLM limits to 128. Even at that, I've been leaving them at 128 when done tuning. Note that the f-body '8746 TBI ECM resets the BLM cells to 128 at every key-on. It is hard-coded in the firmware.

RBob.

 

I have been looking at my XDF and don't really see it. I am using a variant of the 6e expanded XDF. Do you know what it is called or how it may be described? Sorry, but I haven't yet learned how to make changes in hex so if I can't find it or get it into an XDF then it is just out of my reach for now.

 

Look for this parameter:

020005 Title ="Low Lmt for SAM Cell 0 -Set to 128 to force 128 BLM"

There are three others following it. Set them to 128.

RBob.