MCF523X Datasheet, PDF (37/44 Pages) Freescale Semiconductor, Inc – DC Motor with Speed and Current Closed Loops, Driven by eTPU on

CC period
CC
SC
ASDC
PWMF
ASDC
edge_offset
CC activity
SC activity
Software Design
PWM periods
Figure 25. Oscilloscope Screen-shot and Explanation of ASDC, SC, and CC Timing
Figure 25 explains the timing of ASDC, SC, and CC eTPU functions. Signal 4 (green) is the PWM signal
of one base channel, as in Figure 24. Signal 3 (pink) is generated by the ASDC eTPU function. The ASDC
function triggers the AD converter by generating a DMA request on a high-low edge (active low polarity
of ASDC) and simultaneously sending the link to the SC channel every 16th ASDC period (see Figure 25).
The position of the ASDC first edge is synchronized with the beginning of the PWM period. The time
between the PWM period beginning and the ASDC first edge equals to one-quarter of the PWM period.
The ASDC pulse width determines the time necessary to sample the DC-bus current and to transfer this
sampled value to the eTPU data memory. ASDC starts measured sample preprocessing at the time of the
second edge when a sample is supposed to be ready in the eTPU data memory. Immediately after the
DC-bus current sample preprocessing, ASDC function sends the link to the CC channel to start PI
controller calculation. This way the CC synchronization is ensured.
Signal 2 (cyan) is generated by the speed controller (SC) eTPU function. Its pulses determine the activity
of the SC. The pulse width determines the time necessary to calculate the motor speed from a revolution
period measured by the Hall decoder (HD), calculate the required speed ramp, and apply the SC-PI
controller algorithm. The SC output - the new value of desired current - is passed to the current controller.
This calculation is performed periodically at a 1250Hz rate, which is every 16th PWM period.
DC Motor with Speed and Current Closed Loops, Driven by eTPU on MCF523x, Rev. 0
Freescale Semiconductor
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