Rainbow Electronics NUC140 - Manual (Page 40)

NUC140 Series DATA SHEET
Publication Release Date: May 31, 2010
- 40 - Revision V1.02
5.7 PWM Generator and Capture Timer
5.7.1 Introduction
This chip has 4 sets of PWM Generators which can be configured as 8 independent PWM outputs,
PWM0~PWM7, or as 4 complementary PWM pairs, (PWM0, PWM1), (PWM2, PWM3), (PWM4,
PWM5) and (PWM6, PWM7) with 4 programmable dead-zone generators. Each PWM Generator has
one 8-bit prescaler, one clock divider providing 5 divided frequencies (1, 1/2, 1/4, 1/8, 1/16), two PWM
Timers including two clock selectors, two 16-bit PWM down-counters for PWM period control, two 16-
bit comparators for PWM duty control and one dead-zone generator. The 4 sets of PWM Generators
provide eight independent PWM interrupt flags which are set by hardware when the corresponding
PWM period down counter reaches zero. Each PWM interrupt source with its corresponding enable bit
can cause CPU to request PWM interrupt. The PWM generators can be configured as one-shot mode
to produce only one PWM cycle signal or continuous mode to output PWM waveform continuously.
When PCR.DZEN01 is set, PWM0 and PWM1 perform complementary PWM paired function; the
paired PWM timing, period, duty and dead-time are determined by PWM0 timer and Dead-zone
generator 0. Similarly, the complementary PWM pairs of (PWM2, PWM3), (PWM4, PWM5) and
(PWM6, PWM7) are controlled by PWM2, PWM4 and PWM6 timers and Dead-zone generator 2, 4
and 6, respectively.
To prevent PWM driving output pin with unsteady waveform, the 16-bit period down counter and 16-bit
comparator are implemented with double buffer. When user writes data to counter/comparator buffer
registers the updated value will be load into the 16-bit down counter/ comparator at the time down
counter reaching zero. The double buffering feature avoids glitch at PWM outputs.
When the 16-bit period down counter reaches zero, the interrupt request is generated. If PWM-timer is
set as continuous mode, when the down counter reaches zero, it is reloaded with PWM Counter
Register (CNRx) automatically then start decreasing, repeatedly. If the PWM-timer is set as one-shot
mode, the down counter will stop and generate one interrupt request when it reaches zero.
The value of PWM counter comparator is used for pulse width modulation. The counter control logic
changes the output level when down-counter value matches the value of compare register.
The alternate feature of the PWM-timer is digital input Capture function. If Capture function is enabled
the PWM output pin is switched as capture input mode. The Capture0 and PWM0 share one timer
which is included in PWM 0; and the Capture1 and PWM1 share PWM1 timer, and etc. Therefore user
must setup the PWM-timer before enable Capture feature. After capture feature is enabled, the
capture always latched PWM-counter to Capture Rising Latch Register (CRLR) when input channel
has a rising transition and latched PWM-counter to Capture Falling Latch Register (CFLR) when input
channel has a falling transition. Capture channel 0 interrupt is programmable by setting
CCR0.CRL_IE0[1] (Rising latch Interrupt enable) and CCR0.CFL_IE0[2]] (Falling latch Interrupt
enable) to decide the condition of interrupt occur. Capture channel 1 has the same feature by setting
CCR0.CRL_IE1[17] and CCR0.CFL_IE1[18]. And capture channel 2 to channel 7 have the same
feature by setting the corresponding control bits in CCR1 to CCR3. Whenever Capture issues Interrupt
0/1/2/3, the PWM counter 0/1/2/3 will be reload at this moment.