RM0046 Cross Triggering Unit (CTU)
Doc ID 16912 Rev 5 603/936
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:
â—Ź Input signals interface
â—Ź User interface (such as configuration registers)
â—Ź ADC interface
â—Ź Timers interface
The block diagram of the CTU is shown in Figure 301.
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