Chapter 24 Cross Triggering Unit (CTU)
MPC5602P Microcontroller Reference Manual, Rev. 4
Freescale Semiconductor
609
Chapter 24
Cross Triggering Unit (CTU)
24.1
Introduction
In PWM driven systems it is important to schedule the acquisition of the state variables with respect to
PWM cycle. State variables are obtained through the following peripherals: ADC, position counter (for
example, quadrature decoder, resolver and sine-cos sensor) and PWM duty cycle decoder.
The cross triggering unit (CTU) is intended to completely avoid CPU involvement in the time acquisitions
of state variables during the control cycle that can be the PWM cycle, the half PWM cycle or a number of
PWM cycles. In such cases the pre-setting of the acquisition times needs to be completed during the
previous control cycle, where the actual acquisitions are to be made, and a double-buffered structure for
the CTU registers is used, in order to activate the new settings at the beginning of the next control cycle.
Additionally, four FIFOs inside the CTU are available to store the ADC results.
24.2
CTU overview
The CTU receives various incoming signals from different sources (PWM, timers, position decoder and/or
external pins). These signals are then processed to generate as many as eight trigger events. An input can
be a rising edge, a falling edge or both, edges of each incoming signal. The output can be a pulse or a
command (or a stream of consecutive commands for over-sampling support) or both, to one or more
peripherals (for example, ADC or timers).
The CTU interfaces to the following peripherals:
•
PWM—13 inputs
•
eTimer—1 input
•
GPIO—1 external input signal
The 16 input signals are digital signals and the CTU must be able to detect a rising and/or a falling edge
for each of them.
The CTU comprises the following:
•
Input signals interface
•
User interface (such as configuration registers)
•
ADC interface
•
Timers interface
