Syntax:
HPWM channel, frequency, duty cycleCommand Availability:
Only available on Microchip PIC microcontrollers with Capture/Compare/PWM (CCP) module.
This command supports the CCP 8 bit support with Timer 2 only.
For CCP/PWM support for timers 2, 4 and 6, if the specific devices supports alternative CCP/PWM clock sources - see here HPWM_CCPTimerN
For PWM 10 Bit support with other timers - see here HPWM 10 Bit
Explanation:
This command sets up the hardware PWM module of the Microchip PIC microcontroller to generate
a PWM waveform of the given frequency and duty cycle.
If you only need one particular frequency and duty cycle, you should use PWMOn and the constants PWM_Freq and PWM_Duty instead.
channel is 1, 2, 3, 4 or 5, and corresponds to the pins CCP1, CCP2, CCP3, CCP4 and CCP5
respectively. On chips with only one CCP port, pin CCP or CCP1 is always
used, and channel is ignored. (It should be set to 1 anyway to allow
for future upgrades to more powerful microcontrollers.)
frequency sets the frequency of the PWM output. It is measured in KHz.
The maximum value allowed is 255 KHz. The minimum value varies depending
on the clock speed. 1 KHz is the minimum on chips 16 MHz or under and 2
Khz is the lowest possible on 20 MHz chips. In situations that do not
require a specific PWM frequency, the PWM frequency should equal
approximately 1 five-hundredth the clock speed of the microcontroller (ie 40 Khz on
a 20 MHz chip, 16 KHz on an 8 MHz chip). This gives the best duty cycle
resolution possible.
duty cycle specifies the desired duty cycle of the PWM signal, and
ranges from 0 to 255 where 255 is 100% duty cycle.
To stop the PWM signal use the HPWMOff method with the parameter of the channel.
'Stop the CCP/PWM signal
HPWMOff ( 1 )The optional constant HPWM_FAST can be defined to enable the recalculation of the
timer prescaler when needed. This will provide faster operation, but uses extra byte
of RAM and may cause problems if HPWM and PWMOn are used together in a program.
This will not cause any issue when using HPWM and PWMOff in the same program with HPWM_FAST.
The optional constant DisableCCPFixedModePWM can be defined to prevent Timer2 from being enabled. This constant may be required when you need to use Timer2 for non-CCP/PWM
support.
Example:
'This program will alter the brightness of an LED using
'CCP/PWM.
'Select chip model and speed
#chip 16F877A, 20
'Set the CCP1 pin to output mode
DIR PORTC.2 out
'Main code
do
'Turn up brightness over the range
For Bright = 1 to 255
HPWM 1, 40, Bright
wait 10 ms
next
'Turn down brightness over the range
For Bright = 255 to 1 Step -1
HPWM 1, 40, Bright
wait 10 ms
next
loop