Document # 31-0008
LM2_Manual_1.4.doc
24
Since it is often a battle getting an ECU to deliver data fast enough, it is reasonable to
ask why one would lower the priority of a channel? The simple answer is, some ECU
values just do not change very fast. So, reading those values less often means that
values that do change quickly can be read more often. To understand how this works
let’s take a look at how the LM-2 normally reads values:
As we can see from the diagram on the right, values are
read from the ECU one after another, in a loop. Since takes
the
ECU has certain amount of time to respond to each query,
the
longer the list of channels, the longer it takes to complete
the loop. Obviously, the longer to takes to complete the
loop, the larger the time gap between each read of
an
individual value.
Now let’s look at how Low Priority Values fit into this.
Instead of being read once each time through the loop, only one
Low Priority value is read each time through the loop. So, if you
have three low priority values, it will take three passes of the
loop to read them all once.
Read 1st
Value
Read 2nd
Value
Read 3rd
Value
Read last
Value
Repeat
Read 1st
Value
Read 2nd
Value
Read last
Value
Repeat
Read one Low
Priority Value
Low Priority
Value List
