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'FSK on a pic?'
1998\12\16@200626 by tony arkles

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<DIV><FONT color=#000000 size=2>Does anyone know how I might go about making a
PIC into a frequency shifted keying modem?&nbsp; I plan to use it to make some
form of pager but I don't really know how to start..</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT>&nbsp;</DIV>
<DIV><FONT color=#000000 size=2>thx</FONT></DIV></BODY></HTML>

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1998\12\16@234644 by Tjaart van der Walt

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> tony arkles wrote:
>
> Does anyone know how I might go about making a PIC into a frequency shifted keying modem?  I plan
> to use it to make some form of pager but I don't really know how to start..
>
> thx

FSK generation won't be a problem, but the detection will be
a pain in the butt on a PIC.

There is a application note on Scenix's web site for a complete
1200 baud FSK modem. You can get the info from :
ftp://ftp.scenix.com/apps/fsk.src

As a matter if interest, they also have a bells & whistles
application note with :
1) 6 X 19200 baud UARTS
2) 4 X PWM outputs
3) 4 X Independent 16 bit timers
4) 2 X 8 bit A/D
5) 1 X Partridge in a pear tree ;)

on http://www.scenix.com/support/appnotes/index.html

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1998\12\17@170432 by Marc

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> > Does anyone know how I might go about making a PIC into a frequency shifted
keying modem?  I plan
> > to use it to make some form of pager but I don't really know how to start..
>
> FSK generation won't be a problem, but the detection will be
> a pain in the butt on a PIC.
>
> There is a application note on Scenix's web site for a complete
> 1200 baud FSK modem. You can get the info from :
> ftp://ftp.scenix.com/apps/fsk.src

Well I downloaded the file and it contains TX code only.

But I am sure it is no problem to implement FSK receive on a PIC, too.  After al
l it's just 1200
bps. HAMCOM type modems contain a 1-bit A->D and 1 bit math does not require MUL
or DIV
instructions. Although HAMCOM type receivers are not perfect regarding their S/N
requirements
they are used a lot in amateur radio and people can live with it.

If you want to see it proven with code (PIC/SX/AVR), hire me :-)




Regarding pagers: if they are POCSAG you don't need to demodulate the FSK yourse
lf, as the data
directly modulates the UHF carrier. Any FM receiver does the demodulation, so yo
u only
need a comparator (or preferably a treshold device with hysteresis) and a DPLL t
o recover
the bit clock.

1998\12\21@001725 by Tjaart van der Walt

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Marc wrote:
>
> > > Does anyone know how I might go about making a PIC into a frequency shifted keying modem?  I plan
> > > to use it to make some form of pager but I don't really know how to start..
> >
> > FSK generation won't be a problem, but the detection will be
> > a pain in the butt on a PIC.
> >
> > There is a application note on Scenix's web site for a complete
> > 1200 baud FSK modem. You can get the info from :
> > ftp://ftp.scenix.com/apps/fsk.src
>
> Well I downloaded the file and it contains TX code only.

You're right. I looked at their site again, but I also
couldn't find it. Hmmm, I'll look for it again.

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|--------------------------------------------------|
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1998\12\21@002801 by Tjaart van der Walt

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Marc wrote:
>
> > > Does anyone know how I might go about making a PIC into a frequency shifted keying modem?  I plan
> > > to use it to make some form of pager but I don't really know how to start..
> >
> > FSK generation won't be a problem, but the detection will be
> > a pain in the butt on a PIC.
> >
> > There is a application note on Scenix's web site for a complete
> > 1200 baud FSK modem. You can get the info from :
> > ftp://ftp.scenix.com/apps/fsk.src
>
> Well I downloaded the file and it contains TX code only.
>
> But I am sure it is no problem to implement FSK receive on a PIC, too.  After all it's just 1200
> bps. HAMCOM type modems contain a 1-bit A->D and 1 bit math does not require MUL or DIV
> instructions. Although HAMCOM type receivers are not perfect regarding their S/N requirements
> they are used a lot in amateur radio and people can live with it.

I managed to track down the news release. It is a reference
design, so you might have to ask them for it.


Santa Clara, Calif. - Sept. 7, 1998 - Scenix Semiconductor, Inc.
has released a reference design that implements a fully functional
1200-baud FSK/2400-baud DPSK modem in software using the Scenix SX
Series 8-bit microcontroller (MCU). The modem is fully compliant
with Bell 202 and CCITT V.22 bis standards. The reference design,
which also includes DTMF generation and detection and Caller ID
functions, allows engineers to reduce parts count and total system
cost in embedded applications requiring data connectivity, including
point-of-sale terminals, automatic teller machines, answering
machines and remote data gathering and metering systems. The Scenix
SX Series 50 MHz microcontroller is the only 8-bit MCU capable of
fully executing modem functions in software. Until now, software-
implemented modems required a relatively expensive 16- or 32-bit
MCU or digital signal processor (DSP). Other 8-bit MCU solutions
require an external modem chip, increasing both the parts count
and total system cost. The modem reference design replaces external
components with Scenix-designed "Virtual Peripherals." The reference
design incorporates software modules that perform 1200-baud FSK,
2400-baud DPSK and DTMF generation and detection, and Caller ID
functions. Additional Virtual Peripherals, including a 19.2-kbit
UART interface, a 16-bit timer, two pulse-width modulation (PWM)
outputs and an analog-to-digital converter (ADC), are also part
of the modem reference design. Also, because the SX MCU contains
2K x 12 bits of flash/EEPROM, it can be reprogrammed in the field
to incorporate new or enhanced feature sets.

>
> If you want to see it proven with code (PIC/SX/AVR), hire me :-)
For the above specs, SX sure, PIC/AVR no way.

> Regarding pagers: if they are POCSAG you don't need to demodulate the FSK yourself, as the data
> directly modulates the UHF carrier. Any FM receiver does the demodulation, so you only
> need a comparator (or preferably a treshold device with hysteresis) and a DPLL to recover
> the bit clock.

--
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|R&D Engineer : GSM peripheral services development|
|--------------------------------------------------|
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