OMEM710 Hardware Manual 2v11
59
The Alt function is a possible fuel trim, ignition trim, and physical switch output based upon an entry
condition set by the user. The entry condition can be a physical input switch, engine speed, engine
load, throttle position, or a combination of these. The throttle entry condition has separate on/off
values to allow hysteresis. The load and RPM entry conditions have a minimum and maximum
between which the function is ON. For the trims to be available simply on a switch, then set the rpm,
TPS, and load on/off conditions to conditions the engine is always under. For the trims to be active
under certain engine conditions without any switch input then set Alt Function Input to Switch is
Always ON.
Example applications
Nitrous ignition retard
An input to the ECU can be made when the nitrous circuit is complete on one of the AUX IN pins.
The auxiliary input should be set for the Alt Function to AUX n IN (n dependent on the input used) as
shown in the appropriate section of this manual. The ignition retard is then required regardless of
throttle position, engine speed etc, so the values are set as shown below;
VTEC control
Normally, the dedicated VTEC function would be used to control VTEC cams, but some engines
benefit from having the cam to be moved back to the low position at high engine speeds. In this
case, the Alt function must be used. A switch input is not required as the VTEC function is required
all of the time, so the auxiliary input should be set to Switch is always ON as shown in the
appropriate section of this manual. An output is required based on this function so the Alt out option
should be set to one of the auxiliary outputs. The below shows the VTEC used in its most simple
form with just on/off points based on engine speed (on between 3000 and 6500rpm), irrespective of
throttle position and load;
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