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eTPU
The current through the injectors are initially zero since the reaction channel output is in the OFF state as
configured by the DOFF[2:0] field. The eTPU timer window is at the OFF state as well. The modulation
starts when the eTPU channel time window switches to ON state. Modulation phase A starts at this time
as described in
Figure
23-38. The modulation word 0 is used. In this application this phase corresponds to
the Boosted Peak phase. This process allows the fuel injection to start sooner because of the sharp edge of
the current which is important for a precise control of the fuel to be injected. Phase A is the setup to execute
a Threshold-Threshold modulation but note that only I0 value is used since the phase advances when a
certain current is achieved. The following is a description of the bit fields in the Modulation word in order
to execute the modulation described in phase A:
•
LOOP = 0
•
The initial value should be HOD (IOSS = 1)
•
Threshold-Threshold modulation mode is obtained with MM = 00
•
This phase ends when the threshold value I0 is achieved (SM = 11)
•
Necessary to have HOD = 111 for boosted operation and sensor active, LOD setting is not
important in this case since it is not used
•
I0 is read from Threshold Bank by using THRESPT = 0x0 that points to address 0 of this bank
•
I1 is read from Threshold Bank by using (THRESPT + 1) = 0x1
•
Hold-off timer is not used, therefore HDOFFPT can have any value (X)
Freescale Semiconductor
ON
timer
control
signal
OFF
I0
Current in
Injector
I2
I3
I4
I5
A
B
a
b
Figure 23-38. Modulation phases
MPC5644A Microcontroller Reference Manual, Rev. 6
OFF
C
D
c
d
e
Reaction Module (REACM)
time
time
741
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