RC Servo PWM Digital Capture in a Xilinx xc9500 CPLD?

Hello everyone!
Can anyone tell me or suggest a way to capture a RC servo PWM signal with a
Xilinx CPLD in ABEL?. When the pulse duration is 1ms the digital value is
logic 0, when is 2 ms the digital output is a logic 1.

Best Regards
Thanks in advance

Form the signal into a digital value.
Use an external crystal or R/C oscillator to count the width of the pulse.
A count of n in 1ms is a 0, a count of 2n is a 1.  If all you need is a
logical result and not a variable value, this threshold is pretty easy to
program.

"Bruno Cardeira" <bmscc@netcabo.pt> wrote in message
news:40ec6b3b$0$508$a729d347@news.telepac.pt...
> Hello everyone!
> Can anyone tell me or suggest a way to capture a RC servo PWM signal with
a
> Xilinx CPLD in ABEL?. When the pulse duration is 1ms the digital value is
> logic 0, when is 2 ms the digital output is a logic 1.
>
> Best Regards
> Thanks in advance

Bruno Cardeira wrote:
> Hello everyone!
> Can anyone tell me or suggest a way to capture a RC servo PWM signal with a
> Xilinx CPLD in ABEL?. When the pulse duration is 1ms the digital value is
> logic 0, when is 2 ms the digital output is a logic 1.

In building block terms, this is a monostable and a D register.
In a CPLD a monostable is built as an edge-reset-counter-compare.
You could consider hysteresis on the time threshold, as the 1-2ms
windows are usually linear.

If it is multichannel RC, there is a frame signal to consider too.

-jg

thanks for the help john_H and Jim Granville!
It's working!

Bruno

"Jim Granville" <no.spam@designtools.co.nz> escreveu na mensagem
news:W_0Hc.6873$NA1.634567@news02.tsnz.net...
> Bruno Cardeira wrote:
> > Hello everyone!
> > Can anyone tell me or suggest a way to capture a RC servo PWM signal
with a
> > Xilinx CPLD in ABEL?. When the pulse duration is 1ms the digital value
is
> > logic 0, when is 2 ms the digital output is a logic 1.
>
> In building block terms, this is a monostable and a D register.
> In a CPLD a monostable is built as an edge-reset-counter-compare.
> You could consider hysteresis on the time threshold, as the 1-2ms
> windows are usually linear.
>
> If it is multichannel RC, there is a frame signal to consider too.
>
> -jg
>