Re: 1228331 ECU Processor (P4 processor info)

[Ludis Langens <ludis@cruzers.com>]

"Malcolm Robb, LC 0112G" wrote:
> 
> Don't want to be a pain, but my ECU would appear to have RAM from
> 0x0000-0x02FF. Many parts of the code use variable storage in the 0x03XX
> area of memory. Also, one of the first instructions after reset is "lds
>  #$02FF", which I think means load stack pointer = 0x02FF, so I'm assuming
> the stack works down from there.

There is a version of the P4 MPU with (at least) 1K of SRAM.  The chip
number is 16139860 (aka 39860).  It is certainly used in the 16196401
ECM (94-95 3.4 DOHC SFI V6).  The software for that ECM/engine inits the
stack pointer to 0x03ff.  I've seen this same 16139860 in older P4s
where I expected the 512 byte SRAM version.  Some of these might have
been remanufactured units where the MPU was replaced.

> There
> are no references to anything from 0x0300-0x2FFF, although when I dumped
> this area of memory I got images of 0x0000-0x03FF in parts of it. (GM
> saving money by incomplete address decoding ?)

I've been told that the 1228331 ZR1 software also inits the stack to
0x02ff.  Perhaps the 1228331 uses the 512 byte MPU and a little bit of
extra SRAM.  Can you take a picture of the PCB?  Or at least make a
parts list?  I remember you saying that the ECM was hard to get to.

> The code makes reference to some hardware? in the 0x3000- 0x30FF area. The
> values in these locations get transmitted as part of the ALDL data stream.

Those aren't real references to the 0x3??? range.  ALDL data pointers to
double byte values are offset by 0x3000.  This tells the ALDL transmit
function to read both bytes at once in case the double byte value
changes before the second byte gets sent.

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


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