Capture Units
Capture Units
Capture Units
Capture units timestamp transitions on
Capture units timestamp transitions on
capture input pins
capture input pins
Three capture units (per event manager)
Three capture units (per event manager)
-
-
each associated with a capture input pin
each associated with a capture input pin
Timer
Timestamp
Values
Trigger
.
The capture units allow time-based logging of external TTL signal transitions on the capture input
pins. Each C28x event manager (EVA and EVB) has three capture units, two of which are shared
with the quadrature encoder interface circuitry (discussed in next section).
Capture unit #3 on EVA and capture unit #6 on EVB can be configured to trigger an A/D
conversion that is synchronized with an external event. There are several potential advantages to
using the capture for this function over the ADCSOC pin associated with the ADC module. First,
the ADCSOC pin is level triggered, and therefore only low to high external signal transitions can
start a conversion. The capture unit does not suffer from this limitation since it is edge triggered
and can be configured to start a conversion on either rising edges, falling edges, or both. Second,
if the ADCSOC pin is held high longer than one conversion period, a second conversion will be
immediately initiated upon completion of the first. This unwanted second conversion could still
be in progress when a desired conversion is needed. In addition, if the end-of-conversion ADC
interrupt is enabled, this second conversion will trigger an unwanted interrupt upon its
completion. These two problems are not a concern with the capture unit. Finally, the capture unit
can send an interrupt request to the CPU while it simultaneously initiates the A/D conversion.
This can yield a time savings when computations are driven by an external event since the
interrupt allows preliminary calculations to begin at the start-of-conversion, rather than at the
end-of-conversion using the ADC end-of-conversion interrupt. The ADCSOC pin does not offer
a start-of-conversion interrupt. Rather, polling of the ADCSOC bit in the control register would
need to be performed to trap the externally initiated start of conversion.
C28x - Event Manager
7 - 27
Содержание C28 Series
Страница 64: ...Summary 3 16 C28x Peripheral Registers Header Files ...
Страница 78: ...Interrupt Sources 4 14 C28x Reset and Interrupts ...
Страница 218: ...Lab 9 DSP BIOS 9 22 C28x Using DSP BIOS ...
Страница 244: ...Lab 10 Programming the Flash 10 26 C28x System Design ...
Страница 273: ...Appendix A eZdsp F2812 C28x Appendix A eZdsp F2812 A 1 ...
Страница 275: ...Appendix eZdsp F2812 eZdsp F2812 Connector Header and Pin Diagram C28x Appendix A eZdsp F2812 A 3 ...
Страница 276: ...Appendix P2 Expansion Interface A 4 C28x Appendix A eZdsp F2812 ...
Страница 277: ...Appendix P4 P8 P7 I O Interface C28x Appendix A eZdsp F2812 A 5 ...
Страница 278: ...Appendix A 6 C28x Appendix A eZdsp F2812 ...
Страница 279: ...Appendix P5 P9 Analog Interface C28x Appendix A eZdsp F2812 A 7 ...
Страница 281: ...Appendix JP7 JP8 JP11 JP12 Boot Mode Select JP9 PLL Disable DS1 DS2 LEDs C28x Appendix A eZdsp F2812 A 9 ...
Страница 282: ...Appendix A 10 C28x Appendix A eZdsp F2812 TP1 TP2 Test Points ...