base / advance timing - TBI/TPI with distributor

[rrauscher at nni.com]

You are correct with the order of the event, with #2 coming to
TDC starting the triggering the firing of #1.

There are some differences on how the ecm actually handles
the spk firing. The software spark loop runs 80 times a second,
loading the counters on each loop. When a distrib ref pulse
(DRP)happens, the ecm code doesn't do anything different. All
of the dwell times and spark firing times are handled by the
hardware.

There are counters to delay the start of coil charge (dwell),
from the DRP. Then counters for the actual spark firing time.
These counters are loaded asyncronously(sp!) from the DRP. I
hope this helps without clouding the issue.

BobR.

>I have been having a discussion with another gear head about how advance 
>timing is calcualated from the reference pulse generated in the 
>distributor.
>
>Here is how I described it, and would like a reality check.
>
>Pre LS1 small block chevy firing order is 1 8 4 3 6 5 7 2. Firing occurs on

>90 deg. intervals.
>
>Distributor is set for 0 deg (TDC) advance with the timing connector 
>unplugged.
>
>Sequence
>
>1)  # 2 cyl comes upto TDC and a reference pulse is generated, the ecm 
>loads a count value into a timer register based upon current RPM and lookup

>table value ( a lower value == more advance, higher value == less advance).

>
>2) timer reaches 0 generates a timer interrupt, ecm issues a fire pulse to

>the ign. module, #1 cyl. fires xx deg BTDC #1.
>
>3) #1 comes upto TDC and another reference pulse is generated, timer is 
>reloaded for #8 firing event.
>
>
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