The eCAP module can be
used in systems where accurate timing of external events is
important. eCAP/HRCAP on this device is Type-2.
Applications for eCAP
include:
- Speed
measurements of rotating machinery (for example,
toothed sprockets sensed through Hall sensors)
- Elapsed
time measurements between position sensor
pulses
- Period
and duty cycle measurements of pulse train
signals
- Decoding
current or voltage amplitude derived from duty cycle
encoded current/voltage sensors
The eCAP module includes
the following features:
- 4-event
time-stamp registers (each 32 bits)
- Edge-polarity selection for up to four sequenced
time-stamp capture events
- Interrupt
on either of the four events
- Single
shot capture of up to four event timestamps
- Continuous mode capture of timestamps in a
four-deep circular buffer
- Absolute
time-stamp capture
- Difference (Delta) mode time-stamp capture
- All of
the above resources dedicated to a single input
pin
- When not
used in capture mode, the eCAP module can be
configured as a single-channel PWM output
(APWM).
The capture functionality
of the Type-1 eCAP is enhanced from the Type-0 eCAP with the
following added features:
- Event filter
reset bit
- Writing a 1 to ECCTL2[CTRFILTRESET] will clear
the event filter, the modulo counter, and any
pending interrupts flags. Resetting the bit is
useful for initialization and debug.
- Modulo counter
status bits
- The modulo counter (ECCTL2 [MODCTRSTS]) indicates
which capture register will be loaded next. In the
Type-0 eCAP, it was not possible to know current
state of modulo counter.
- DMA trigger
source
- eCAPxDMA is added as a DMA trigger. CEVT[1–4] can
be configured as the source for eCAPxDMA.
- Input multiplexer
- ECCTL0 [INPUTSEL] selects one of 128 input
signals.
- EALLOW protection
- EALLOW protection is added to critical registers.
To maintain software compatibility with the Type-0
eCAP, configure DEV_CFG_REGS.ECAPTYPE to make
these registers unprotected.
The capture functionality
of the Type-2 eCAP is enhanced from the Type-1 eCAP with the
following added features:
- ECAPxSYNCINSEL
register
- The ECAPSxYNCINSEL register is added for each
eCAP to select an external SYNCIN. Every eCAP can
have a separate SYNCIN signal.
The eCAP inputs connect to
any GPIO input through the Input X-BAR. The APWM outputs connect to
GPIO pins through the Output X-BAR to OUTPUTx positions in the GPIO
mux. See Section 5.4.3 and Section 5.4.4.
The eCAP module is clocked
by PERx.SYSCLK.
The clock enable bits
(ECAP1–ECAP3) in the PCLKCR3 register turn off the eCAP module
individually (for low-power operation). Upon reset, ECAP1ENCLK is
set to low, indicating that the peripheral clock is off.