NXP Semiconductors MPC5644A, Reference Manual, Page: 727 / 1735

Reaction Module (REACM)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor 727
23.5 Modulation Modes
This section describes the modulation modes provided by the reaction module.
23.5.1 Threshold/Threshold mode
This mode is programmed by using REACM_MCWBx[MM] = 00. In this modulation mode the reaction
channel tries to maintain the ADC results between two threshold limits. The modulation actions are as
follows:
• ADC result

[THRESPT]: The reaction channel turns the outputs off by loading LOD[2:0] to the
channel outputs.
• ADC result < [T 1]: The reaction channel turns the outputs on by loading HOD[2:0] to
the channel outputs.
• [T 1]

ADC result < [THRESPT]: The reaction channel keeps the outputs unchanged.
Figure 23-27 indicates the threshold/threshold modulation mode.
Figure 23-27. Threshold/threshold modulation mode
There can be overshoots or undershoots in the real application related to the threshold limits. This occurs
due to following:
1. Feedback values are periodically sampled thus can present gaps on the measured values, for
example when the sample occurs the value already passed the range defined by the limits.
2. There is a delay between the sampling of feedback value and the reaction of the reaction channel.
This is mainly caused by the ADC conversion time and its maximum sampling frequency.
23.5.2 Threshold/Hold-off mode
This modulation mode is programmed by using REACM_MCWBx[MM] = 01. In this mode the output
pins are driven with HOD[2:0] until the ADC results matches or is greater than the programmed Threshold.
The output controls are then driven with LOD[2:0] for a fixed amount of time defined by the hold-off
timer. Note that the upper threshold limit and the hold-off timer pointer are indicated by the modulation
word in the REACM_MCR register.
Injector
time
Upper Limit
Lower Limit
feedback
set output to LOD
set output to HOD
I