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Topic 5 The Analog Subsystem Slide 8

This slide shows the conversion triggers. A 32x8 MUX is shown as an example. All of the trigger sources that are coming into this MUX are coming from the C28X, the three available CPU timers, the GPIO MUX that can start a conversion trigger, and then all of the ePWM modules, one through nine. Each of the ePWM modules has a start of conversion A and B and also ePWM sync signals that could be used for the ramp generator for slope compensation. The Concerto ePWM has been redesigned and one of the new features is that instead of two compare registers there are four compare registers. This can be useful to determine the exact placement of the start of conversion point for the ADC. Typical placement for the start of conversion point is at the mid-point of the PWM, it could be either at the peak or the valley. Some applications desire to have it slightly delayed from a compare match; this is because there is typically noise from the compare event, and in order to avoid passing that to the inverter, some delay is needed to keep the sampling as close as possible to the compare event while avoiding the noise. Having the exact placement of the start of conversion point to be able to compensate for jitter in your system is very useful as well. With Concerto, there are a number of trigger sources available. These are managed by the eight trigger select registers, and there are five bits for each of the registers. The user can choose the personality of these eight trigger lines based upon the configuration of the registers. All eight of the triggers are shared both by ADC1 and ADC2, therefore it is possible to have four signals being sampled simultaneously by a single ePWM trigger. The sample-and-hold windows will start at the same moment in time for four different analog signals.

PTM Published on: 2012-02-23