Texas Instruments TMS320x28xx, 28xxx manual 41. Event-Trigger Interrupt Generator, input =

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Event-Trigger (ET) Submodule

The number of events that have occurred can be read from the interrupt event counter (ETPS[INTCNT]) register bits. That is, when the specified event occurs the ETPS[INTCNT] bits are incremented until they reach the value specified by ETPS[INTPRD]. When ETPS[INTCNT] = ETPS[INTPRD] the counter stops counting and its output is set. The counter is only cleared when an interrupt is sent to the PIE.

When ETPS[INTCNT] reaches ETPS[INTPRD] the one of the following behaviors will occur:

∙If interrupts are enabled, ETSEL[INTEN] = 1 and the interrupt flag is clear, ETFLG[INT] = 0, then an interrupt pulse is generated and the interrupt flag is set, ETFLG[INT] = 1, and the event counter is cleared ETPS[INTCNT] = 0. The counter will begin counting events again.

∙If interrupts are disabled, ETSEL[INTEN] = 0, or the interrupt flag is set, ETFLG[INT] = 1, the counter stops counting events when it reaches the period value ETPS[INTCNT] = ETPS[INTPRD].

∙If interrupts are enabled, but the interrupt flag is already set, then the counter will hold its output high until the ENTFLG[INT] flag is cleared. This allows for one interrupt to be pending while one is serviced.

Writing to the INTPRD bits will automatically clear the counter INTCNT = 0 and the counter output will be reset (so no interrupts are generated). Writing a 1 to the ETFRC[INT] bit will increment the event counter INTCNT. The counter will behave as described above when INTCNT = INTPRD. When INTPRD = 0, the counter is disabled and hence no events will be detected and the ETFRC[INT] bit is also ignored.

The above definition means that you can generate an interrupt on every event, on every second event, or on every third event. An interrupt cannot be generated on every fourth or more events.

Figure 2-41. Event-Trigger Interrupt Generator

ETCLR[INT]

EPWMxINT

Clear
Latch		ETFLG[INT]
Set
		ETPS[INTCNT]
Generate	1	0
interrupt		Clear CNT
pulse		2-bit
when	0
		Counter
input = 1

Inc CNT

ETSEL[INT]

ETPS[INTPRD]

ETSEL[INTSEL]

ETFRC[INT]

000 0

001 CTR=Zero

010 CTR=PRD

011 0

100 CTRU=CMPA

101 CTRD=CMPA

101 CTRU=CMPB

111 CTRD=CMPB

Figure 2-42shows the operation of the event-trigger's start-of-conversion-A (SOCA) pulse generator. The ETPS[SOCACNT] counter and ETPS[SOCAPRD] period values behave similarly to the interrupt generator except that the pulses are continuously generated. That is, the pulse flag ETFLG[SOCA] is latched when a pulse is generated, but it does not stop further pulse generation. The enable/disable bit ETSEL[SOCAEN] stops pulse generation, but input events can still be counted until the period value is reached as with the interrupt generation logic. The event that will trigger an SOCA and SOCB pulse can be configured separately in the ETSEL[SOCASEL] and ETSEL[SOCBSEL] bits. The possible events are the same events that can be specified for the interrupt generation logic.

66 ePWM Submodules SPRU791D–November 2004–Revised October 2007

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