There are six identical eCAP modules in Concerto devices: eCAP1, 2, 3, 4, 5, and 6. Each eCAP module represents one complete capture channel. Its main function is to accurately capture the timings of external events. One can also use eCAP modules for PWM, when they are not being used for input captures. This secondary function is selected by flipping the CAP/APWM bit of the ECCTL2 Register. For PWM function, the counter operates in count-up mode, providing a time base for asymmetrical pulse width (PWM) waveforms. The CAP1 and CAP2 registers become the period and compare registers, respectively; while the CAP3 and CAP4 registers become the shadow registers of the main period and capture registers, respectively.
The left side of Figure 5-46 shows internal components associated with the capture block, and the right side depicts the PWM block. The two blocks share a set of four registers that are used in both Capture and PWM modes. Other components include the Counter block that uses the SYNCIN and SYNCOUT ports to synchronize with other modules; and the Interrupt Trigger and Flag Control block that sends Capture, PWM, and Counter events to the C28x PIE block through the ECAPxINT output. There are six ECAPxINT interrupts—one for each eCAP module.
The eCAP peripherals are clocked by C28SYSCLK, and its registers are accessible by the C28x CPU. This peripheral clock can be enabled or disabled by flipping a bit in one of the system control registers.