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'synchronous data transmission....'
1999\07\10@153547 by Dan Tye

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A little help?   I'm prototyping a callerid system in which I need to
send a stream of data from a PIC17c756 through an mxcom mx614 to a
standard callerid box (the 614 is just a bell 202 compatible modem ic).
The problem is that I don't really understand the communication protocol
I need to use.... yes, this is the first time I've done this.....  I've
done Async stuff before, but the problem is I have to send the callerid
box a 300bit stream of continuous, alternating 1s and 0s and async has
start and stop bits and wait time between characters etc that screw this
whole thing up.

So, I assume that I must use the synchronous mode of data transmission,
and as I understand it, this means getting my sender (the PIC) and the
receiver (the modem) handshaking at the same rate, and I don't know how
to do this or even if I need to.  Anybody want to lend me some of their
experience here?

Thanks!

+++++++++++++++++++++++++++++++++++++++
++      Dan Tye
++
++      Tel-Tron Technologies Corporation
++      220 Fentress Boulevard
++      Daytona Beach, FL 32114
++      Phone: 904-255-1921    Fax: 904-258-3782
+++++++++++++++++++++++++++++++++++++++

1999\07\10@154844 by CUTTLER!

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Ok, this is a simple one.
Dont do what you are doing.

Go to  http://www.mitelsemi.com/
and look up the MT8843

It does everything for you.
The unit can either send you the data Via ascyn or sync.

Muuuuch easier than trying to get a modem chip to do it.


>So, I assume that I must use the synchronous mode of data transmission,
>and as I understand it, this means getting my sender (the PIC) and the
>receiver (the modem) handshaking at the same rate, and I don't know how

1999\07\10@155050 by A Rudzki

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Hello Dan,

I don't think so.  With synchronous communication, either the PIC is the
master (it provides the clock), or slave, in which case the chip connected
to the PIC provides the clock.  If the PIC is in slave mode, you don't set
up its clock rate, it collects data bits based on the incoming clock
waveform.


tony

1999\07\10@191300 by Mike Keitz

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On Sat, 10 Jul 1999 15:24:54 -0400 Dan Tye <spam_OUTdtyeTakeThisOuTspamTEL-TRON.COM> writes:
>A little help?   I'm prototyping a callerid system in which I need to
>send a stream of data from a PIC17c756 through an mxcom mx614 to a
>standard callerid box (the 614 is just a bell 202 compatible modem
>ic).

I haven't actually done any caller ID, but according to the notes in the
MC145447 data sheet it is async.  Although it is easy to send at 1200
baud with software, a PIC's built in async hardware is also suitable.  If
you send 30 0xAA characters at 8-N-1 as fast as possible you will get the
required alternating bits.  (A start bit is a 0 and a stop bit is a 1, so
you're sending 0101010101 each time 0xAA is loaded).

It is possible (but not particularly easy) to send without a modem chip.
Use a resistor DAC on the port pins and generate sine waves with
software.  This method is not recommended for beginners.

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1999\07\30@150714 by Dan Tye

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Thanks Mike!  In general, your suggestion solved my problem, the only
change required was to send 0x55 instead of 0xaa because lsb is
transmitted first.  I did finally get the callerid box to display my
information.  I almost cried.  Simple enough project, but my first with
a PIC.  Thanks again.

Now comes problem number 2!  Asynch solved problem #1, but now I
definitely can't weasel out of using synchronous communication.  I have
a tone generation IC, an MX803A, that I need to transmit 2 unique,
nonstandard audio tones to a remote receiver via PSTN.  Problem is, the
803A stores the frequency, timing information, and control signals in
internal registers that I have to write to synchronously.  I am using
MPLAB C-17 and a 17c752 to do this project, and I'm having difficulty
finding out where to begin.  Any suggestions?

-dan


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