I haven't used the TI part but I have used the Maxim MAX3222 which has a
different pin out (doesn't have the two no connect pins) but is electrically
equivalent.

It doesn't require anything special for capacitors, I use cheap ceramics.

I'd check that the not_en pin is low, the not_pwrdown pin is high and, that
the transmitter outputs are not shorted. If that doesn't find the problem
I'd try a new chip.

Paul

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Mike Hord
> Sent: Thursday, November 06, 2003 11:01 PM
>
> Has anyone successfully used the TI SN75C3222 for RS232 level
> shifting?  I'm having a rough time with it, and I really don't want
> to replace the one on my prototype PCB if I don't have to.
>
> Everything looks good-ish, except for some reason, I don't get
> the +/- 5V out of the charge pump.  I get +/-2.5V or so.  My
> input voltage looks good, the enable inputs are set right.
>
> I'm not getting any kind of output, just a flat line at ground.
> Any ideas?  Is there something I'm missing?  I've got .1uF
> ceramic caps; the datasheet doesn't specify anything about
> what kind of caps to use, just .1uF for 3.3V +/- .3V.  I've
> tried adding an additional capacitor to each one, and using
> both 3.15V (the desired final voltage) and 3.3V.
>
> Any ideas?  Find a Maxim part, maybe? ;-)
>
> Mike H.

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