SM8223 appears it need +3V. So you need an RS232 transciever which run at 3V.
http://www.npcamerica.com/pdf/SM8223.pdf

On 9/14/07, mamad876 <mamadharab@gmail.com> wrote:
>
> Hi all,
>
> Recently I made a Caller ID decoder using SM8223 chip and I decided to
> connect it's out put to computer serial port and I bought a MAX232 chip and
> I made a prototype board regarding to it's data sheet.
> My problem is when I use my decoder separately it works well (I think
> because actually I don't see the result but I can see the CID found signal
> with an LED connected to board) but just when I connect ANY PINS of my RS232
> converter to the CID board (Even GND wire of my RS232 Pro board) it stops
> working (ie. LED doesn't show CID signal ). I tried to separate the Power
> supply of my boards but this time the same problem when connecting TxD (ie
> T1 pin) of MAX232 to CID decoder serial output was exists.
>
> NOTE:
> I tested my RS232 board with another board with PIC16f84 and it works fine!
>
> Does any one have a suggestion.
>
> Thanks in advance.
> MAMAD
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