With the diodes oriented that way the resistor should go to ground:

 AND gate ->|---
                |
GND--/\/1k\/\---------- pin 10 max 232
                |
 AND gate ->|---

Thus either gate can pull pin 10 high, and the resistor will pull pin 10
low when the gates are low.  Without the resistor pin 10 will remain
high when both gates are low until diode leakage pulls it down, which
could take many milliseconds.  If you used NAND gates (idle high) you
would turn the diodes around and run the resistor to +5V.

Sherpa Doug

> -----Original Message-----
> From: Keith Christopher [mailto:keithc_21211@YAHOO.COM]
> Sent: Thursday, January 24, 2002 6:36 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE] Little 232 help
>
>
> So this would be a resistor from pin 10 to +5 ?
> remember the diodes are
>
> AND gate ->|---
>                |
>                --- pin 10 max 232
>                |
> AND gate ->|---
>
>
> Only one And gate open at a time.
>
> So you're saying
>
> AND gate ->|---
>                |
> +5--/\/1k\/\---------- pin 10 max 232
>                |
> AND gate ->|---
>
> ?
> Keith
> --- Douglas Butler <dbutler@IMETRIX.COM> wrote:
> > Just a stupid suggestion:  You have diodes to turn
> > the MAX232 ON (or
> > OFF), but do you have a resistor to drag the MAX232
> > input the other way
> > when neither diode is conducting?  Something like 1K
> > for starters.
> >
> > Sherpa Doug
> >
> > > -----Original Message-----
> > > From: Keith Christopher
> > [mailto:keithc_21211@YAHOO.COM]
> > > Sent: Thursday, January 24, 2002 3:47 PM
> > > To: PICLIST@MITVMA.MIT.EDU
> > > Subject: [EE] Little 232 help
> > >
> > >
> > > I have a 2 logic gates going to the rx pin (ttl)
> > on a
> > > max 232 chip. I have put 1n4148 diodes between the
> > > logic outs (only one gate open at a time), and I
> > > receive no output on the PC connected to the 232
> > side
> > > of the max232. If I remove the diodes and hook
> > both
> > > gate outputs to the pin (pin 10) I get nothing
> > also.
> > > If I hook them up one at a time All is well. Not
> > sure
> > > why the diodes are not working as I figure they
> > would.
> > > I have checked the voltages and one is at 4.94v
> > the
> > > other is 33mV, without the diodes.
> > >
> > >
> > > Keith
> > >
> > > __________________________________________________
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