Enhanced Time Processing Unit (eTPU2)
MPC5644A Microcontroller Reference Manual, Rev. 6
904
Freescale Semiconductor
Figure 24-58. Normal Mode
24.5.7.5.2
Halt mode (Deceleration)
In case of deceleration, the Tooth Tick Counter reaches the TICKS value before the arrival of the next
tooth. The Count Control logic does not reset neither advances TCR2 and Tooth Tick Counters. The Count
Control logic halts TCR2 and Tooth Tick Counters at the end of the tooth, waiting for the physical tooth
to arrive.
When the physical tooth is detected the EAC switches back to Normal Mode and releases TCR2 to count
the angle ticks of the new tooth, also resetting the Tooth Tick Counter. Only then TCR2 may wrap to 0, if
TPR bit LAST is asserted. See
for a detailed diagram of Halt Mode behavior.
The microcode service caused by the physical tooth determines the deceleration, calculates the new tooth
period and Angle Tick period and updates TRR. This operation slows the angle tick rate generated by the
Angle Tick Generator on-the-fly, to the rate required for the new tooth period.
Since the microcode service is initiated by the physical tooth edge, microcode latency may introduce a
small angle error caused by using the TRR value of the previous tooth at the beginning of the current tooth.
On high RPM, deceleration is relatively small but the microcode latency may take a significant percentage
of the tooth period. On low RPM microcode service latency takes little percentage of the tooth period, but
there may be cases of extreme acceleration and deceleration. The microcode latency can be calculated
knowing TCR1 value during the service time, and TCR1 value captured in the EAC channel due to the
physical tooth pin transition. The duration of the Halt mode is obtained using the estimated tooth time.
Tooth Signal
Angle Tick
TRR
P1
P2
P3
P4
Tooth Tick Count
EAC Channel
Service Time Slot
EAC Channel
Capture
TCR1
TCR1
TCR1
TCR1
P1/ n
P2/ n
P3/ n
y
y+n
y+n+1
Ch0
Ch0
Ch0
*service request
**microcode updates TRR
*
*
**
**
TCR2 - continuous
0
0
0
Summary of Contents for MPC5644A
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