> Hi, well for a start sorry about my first post...i
> didn't make things too clear. I checked the archives
> but couldn't find anything that helped.
>
> What I need is some code (pic assembly) for a PC16C74A
> to implement the following....
>
> **Generate two square wave outputs, each with a 50%
> duty cycle. Also I want to be able to vary the
> frequency of these signals independently of one and
> other from about 1KHz to 2MHz or as close as I can get
> to these limits.
>
> **The frequency of each square wave will be entered on
> a PC keyboard and sent via the serial port to the PIC
> but at the moment my main problem is trying to set up
> the square waves themselves.
>
> If anyone has some code that I could use to generate
> these square waves and set their frequencies by say
> putting a value in the appropriate register I'd really
> appreciate it. Thanks a million,
>                                 John.
>
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>
>john darcy wrote:
>
>> Hi, well for a start sorry about my first post...i
>> didn't make things too clear. I checked the archives
>> but couldn't find anything that helped.
>>
>> What I need is some code (pic assembly) for a PC16C74A
>> to implement the following....
>>
>> **Generate two square wave outputs, each with a 50%
>> duty cycle. Also I want to be able to vary the
>> frequency of these signals independently of one and
>> other from about 1KHz to 2MHz or as close as I can get
>> to these limits.
>>
>> **The frequency of each square wave will be entered on
>> a PC keyboard and sent via the serial port to the PIC
>> but at the moment my main problem is trying to set up
>> the square waves themselves.
>>
>> If anyone has some code that I could use to generate
>> these square waves and set their frequencies by say
>> putting a value in the appropriate register I'd really
>> appreciate it. Thanks a million,
>>                                 John.
>>

>
> the xor trick to double the freq results in a waveform that has pulses at
> each edge
> of the original signal. If you need a square wave out, you could always
> quadruple the
> signal and feed the result into a flipflop to restore a 50% duty cycle.
>
> =======================================================
> Lawrence Glaister VE7IT             email: lgKILLspamjfm.bc.ca
> 1462 Madrona Drive                  http://jfm.bc.ca
> Nanoose Bay BC Canada
> V9P 9C9
> =======================================================

>Dan Michaels wrote:
>>
>> Mike Harrison wrote:
>>
>> >>With 10Mhz xtal, you can get 2.500 Mhz down to 600 hz - it obviously
>> >>scales by xtal value. Frequency selections are a little "grainy"
>> >>on the high end - 2.5, 1.25, .8333, .625, .500, .4166, .357, .275,
>> >>.250, etc. However, rock-steady pulse generation.
>>
>> >If by 'rock steady' you mean zero jitter, you can do this using timer
>> >interrupts, with Fosc/4 resolution.
>> >
>>
>> By rock-steady, I meant it is generated in h.w., and once set,
>> doesn't even burp when any other s.w. is running. Just try generating
>> a 1 Mhz square-wave in s.w. simultaneous with RS-232 comms.
>
>If the extra hardware is not too much, maybe an external phase locked
>loop circuit would be in order.
>

> David-embedded wrote:
> >Dan Michaels wrote:
> >>
> >> Mike Harrison wrote:
> >>
> >> >>With 10Mhz xtal, you can get 2.500 Mhz down to
> 600 hz - it obviously
> >> >>scales by xtal value. Frequency selections are
> a little "grainy"
> >> >>on the high end - 2.5, 1.25, .8333, .625, .500,
> .4166, .357, .275,
> >> >>.250, etc. However, rock-steady pulse
> generation.
> >>
> >> >If by 'rock steady' you mean zero jitter, you
> can do this using timer
> >> >interrupts, with Fosc/4 resolution.
> >> >
> >>
> >> By rock-steady, I meant it is generated in h.w.,
> and once set,
> >> doesn't even burp when any other s.w. is running.
> Just try generating
> >> a 1 Mhz square-wave in s.w. simultaneous with
> RS-232 comms.
> >
> >If the extra hardware is not too much, maybe an
> external phase locked
> >loop circuit would be in order.
> >
>
>
> Extra h.w. is probably ok for some. Am enclosing the
> PLL ckt
> Jinx sent me offlist - I imagine he won't mind -[am
> sure it
> came out of a book anyways - say what, J ???].
>
> Another 1-chip solution came to mind. A Scenix
> running at 50
> Mhz could probably handle a "finely-tuned" VP
> [virtual peripheral]
> that could both generate two square-waves to 1 Mhz
> and also perform
> RS-232 simultaneously, without burping the
> square-waves.
>
> - danM
>

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