----- Original Message -----
From: "harshit suri" <suri_list@YAHOO.COM>

> I need a chip that gives me 4 channels of PWM . I want
> 4 simultaneously
> operating PWM channels.

I think Einstein wrestled with this problem once... something about standing
on a hill when two lightning bolts flash with a mirror to figure out if they
were really simultaneous?

>Preferable frequency of
> generation should be greater
> than 50 Khz.

Ooooh! so not really simultaneous after all!

> I wish to have at least 8 bits of resolution PER
> channel. meaning 256 levels
> of speed control (The application is DC motor speed
> control)
> I wasn't being able to find a cheap solution. so i
> thought id buy a cheap
> PIC. Program it so that my main microcontroller can
> send commands to the PIC
> to adjust the speed levels.

Sounds good, but remember that most pics can only source or sink about 20mA,
so it would require an external amplifier for driving most motors.

> I was looking at the microship site and prefered the
> flash devices as they
> are reprogrammable.

Programmable microships?  Sign me up!

> I found the PIC18F448 Family : it had 5 PWMs
> advertised. But it seemed an
> overkill as it was a 40 pin device.(I prefer DIPs).

PWM doesn't have to be done in hardware.  It's not too hard to bit bang, and
if you have a dedicated pic for it anyway... how else are you going to use
all those processing cycles?  The hardest part will be to communicate the
speed for four different channels to the pic - how are you planning on doing
that?  You need to specify what sort of signals you'll be expecting for
input (analog? serial? parallel?) before you can select a suitable chip.

> I have never worked with PICs before. But do know they
> are cheap and simple
> devices to work with
> 1)Pls suggest a chip : any chip which can do the
> above. and has minimal I/o
> and is cheap :-)

Sounds like any chip with more than 8 I/O pins could do it in some form or
fashion.  200khz of bandwidth (4x50khz) takes up only 4% of the available
instruction cycles on a pic running at 20mhz, leaving quite a few cycles to
sample your input, do some math, then generate PWM on the output.
Transferring 32 bits of resolution into the chip through a serial interface
would probably be one of the biggest time consumers, but it won't break the
project by any means.

Pick a chip with a USART that can oscillate at 20 mhz and has at least 4
pins left over for outputs, and that should get you started.  The 16F62x is
a good candidate.

> 2)Can anyone give code for the same.

Maybe we could program the chip and mail it to you as well? ;)

> Thanks

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.