I have read 84ELKY's post on the knock count problem and pored through the aujp code. I seems clear that knock count is stored at 0x$3FCA but I can find nowhere that it is written to this location. I see the code that reads U6 but it only seems to be invoked to test for sensor fault.

Can anyone point me to the 'read' code. I suspect that when the value is read from the ADC chip some lower threshold must be exceeded before it counts as knock.

Thanks

 

The address of $3FCA accesses hardware. It is the location of the PA3 (knock) counter.

RBob.

 

Okay that answers one big question.
Can you explain how the signal gets from U6 channel 3 to this hardware location. Is there a loop somewhere that does that? Updating all the inputs from U6 and U5 ?

Thanks again
Bob

 

There is a subroutine at the bottom of the code that reads the input.
When called the parameters like channel number are set as register variables and the code executes using them and returns with the input value.
Search U5 or U6 channel and something should indicate the routine that is jumped to after setting a the register values (LDA or something similar)
Jp

 

As to your original Q, the value is a double word storage location and the "count" value is the upper byte IIRC.
By looking at the lower byte you can see the actual knock counter indication of knocks increasing (and effectively retarding the timing) before the "standard" byte indicates.
HTH

 

It doesn't. U6 is an analog MUX used for inputs to the ADC device (U5). The knock sensor is connected to the U6 channel 3, not the knock filter. This allows the ECM to test the resistance of the knock sensor and the wire from it to the ECM.

The output of the knock filter goes to the ECM PA3 hardware counter.

RBob.

 

More questions for Rbob.

Okay so my understanding increases..
when you say "the knock filter goes to the ECM PA3 hardware counter"
are you refering to pin 42 on U2?

Does this mean that the output from the knock filter is a digital signal?
May have to put scope on a knock filter on the bench.
Do you happen to know what the input voltage to the filter (pin 32 i think) is so I can bench test one I have removed from the Memcal?

Thanks again
Bob Workman

 

Yes.

Yes.

+12 volts via a 30 ohm resistor, see sheet 9.

On the MEMCAL, pin 29 is the input from the sensor. Pin 30 is power, pin 31 is ground, with pin 32 being the output to the PA3 counter.

The other knock filter pins aren't used within the ECM.

RBob.

 

Thanks for the great info!

So this is going to require a bit of a project rethink but each step gets me a little bit closer.