>-----Original Message-----
>From: Stefano Vanzo [mailto:microchip@VANZO.IT]
>Sent: 28 January 2004 08:15
>To: PICLIST@MITVMA.MIT.EDU
>Subject: [PIC:] Vref+, VDD and PWM on PIC16f818
>
>
>Hello everyone,
>        Thanks for reading. I am starting with PWM and have 2
>questions about this project:
>        1 analog input with 4.096 Volt ref+
>        1 PWM
>        3 digital pins for digital byte output of the analog value
>
>First question, if i use PWM with FFFF output will it give me
>4.096 volts, 5 volts or will it be unknown

Firstly, the CCP module has a maximum resolution of 10bits in PWM mode, so
0xFFFF is not a valid duty cycle setting.  The actual resolution you get
depends on the PWM period you choose (the data sheet shows the relationship
between resolution and period).

The PWM output has a voltage swing limited by the Vss and Vdd rails, so with
100% duty cycle, the output will be at Vdd (which may be 5 volts in your
case).  The Vref input is only for the A/D converter.

>Second question
>after I started PWM does it keep on going by it's own or do i
>have to keep on givig it an input to "keep it alive"
>

You don't have to keep giving it an input, there is no overhead in operating
the CCP module in PWM mode.  You simply configure the module for PWM
operation, set the duty cyclce and it will continue working until power is
removed.

Regards

Mike





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