C8051F58X Datasheet, PDF (319/356 Pages) Silicon Laboratories – Programmable hysteresis and response time Configurble as interrupt or reset source Low current

C8051F58x/F59x
Write to
PCA0CPLn
0
ENB
Reset
Write to
PCA0CPHn ^ENB
1
PCA0CPMn
P ECCMT P E
WCA A AOWC
MOP P TGMC
1 MPN n n n F
6nnn
n
n
x 000
x
PCA0CPLn
Enable
8-bit
Comparator
8-bit Adder
PCA0CPHn
Adder
Enable
Toggle
match
TOGn
0 _{CEXn Crossbar}
1
Port I/O
PCA0 Timebase
PCA0L
Figure 28.7. PCA0 Frequency Output Mode
28.3.5. 8-bit, 9-bit, 10-bit and 11-bit Pulse Width Modulator Modes
Each module can be used independently to generate a pulse width modulated (PWM) output on its associ-
ated CEXn pin. The frequency of the output is dependent on the timebase for the PCA0 counter/timer, and
the setting of the PWM cycle length (8, 9, 10 or 11-bits). For backwards-compatibility with the 8-bit PWM
mode available on other devices, the 8-bit PWM mode operates slightly different than 9, 10 and 11-bit
PWM modes. It is important to note that all channels configured for 8/9/10/11-bit PWM mode will use
the same cycle length. It is not possible to configure one channel for 8-bit PWM mode and another for 11-
bit mode (for example). However, other PCA0 channels can be configured to Pin Capture, High-Speed
Output, Software Timer, Frequency Output, or 16-bit PWM mode independently.
28.3.5.1. 8-bit Pulse Width Modulator Mode
The duty cycle of the PWM output signal in 8-bit PWM mode is varied using the module's PCA0CPLn cap-
ture/compare register. When the value in the low byte of the PCA0 counter/timer (PCA0L) is equal to the
value in PCA0CPLn, the output on the CEXn pin will be set. When the count value in PCA0L overflows, the
CEXn output will be reset (see Figure 28.8). Also, when the counter/timer low byte (PCA0L) overflows from
0xFF to 0x00, PCA0CPLn is reloaded automatically with the value stored in the module’s capture/compare
high byte (PCA0CPHn) without software intervention. Setting the ECOMn and PWMn bits in the
PCA0CPMn register, and setting the CLSEL bits in register PCA0PWM to 00b enables 8-Bit Pulse Width
Modulator mode. If the MATn bit is set to 1, the CCFn flag for the module will be set each time an 8-bit
comparator match (rising edge) occurs. The COVF flag in PCA0PWM can be used to detect the overflow
(falling edge), which will occur every 256 PCA0 clock cycles. The duty cycle for 8-Bit PWM Mode is given
in Equation 28.2.
Important Note About Capture/Compare Registers: When writing a 16-bit value to the PCA0 Cap-
ture/Compare registers, the low byte should always be written first. Writing to PCA0CPLn clears the
ECOMn bit to 0; writing to PCA0CPHn sets ECOMn to 1.
Duty Cycle = ^---2---5----6----^–-----P----C-----A----0----C-----P----H-----n----^
256
Equation 28.2. 8-Bit PWM Duty Cycle
Using Equation 28.2, the largest duty cycle is 100% (PCA0CPHn = 0), and the smallest duty cycle is
0.39% (PCA0CPHn = 0xFF). A 0% duty cycle may be generated by clearing the ECOMn bit to 0.
Rev. 1.2
319