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'[PIC]: ICD RS232 at 3V'
2000\06\30@041901 by Alan B. Pearce

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Someone recently was making mutterings about possible problems using the ICD at
3V, but the max232 is only spec'd for 5V. Maxim have a 3 to 5.5V replacement
chip which is pin compatible to the MAX232, and so should drop into the ICD
without any trouble. The only gotcha would seem to be to take care with the
capacitor values in the voltage multiplying section of the chip - see the data
sheet. The maxim part number is MAX3232E. Maxim web site at
http://www.maxim-ic.com

2000\06\30@115813 by Don B. Roadman

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On 30 Jun 2000, at 9:17, Alan B. Pearce wrote:

> Someone recently was making mutterings about possible problems using
> the ICD at 3V, but the max232 is only spec'd for 5V. Maxim have a 3 to
> 5.5V replacement chip which is pin compatible to the MAX232, and so
> should drop into the ICD without any trouble. The only gotcha would
> seem to be to take care with the capacitor values in the voltage
> multiplying section of the chip - see the data sheet. The maxim part
> number is MAX3232E. Maxim web site at http://www.maxim-ic.com
>
Yes, and I remember someone who posted that he had talked to a
microchip guy at a seminar who told him that the max chip was the
first thing in the ICD to crap out at about 3 volts, so apparently
they'll run with less than 5V. I ordered my parts from Jamco, who
dont have the 3232, so I'll end up using a 232, but I noticed that
they were pin compatible so maybe I can swap them out some
day. I also dont under stand the caps, they call for 1uF for the 232
and .1uF for the 232A. One would think there would be a range of
cap values, perhaps with a tradeoff curve to indicate maybe less
ouput drive capability or something. They sure seem to have
minimalist data sheets :)

2000\06\30@122625 by James Paul

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All,

A Maxim rep once told me, or maybe I read it in some literature
somewhere that the charge pump is different in the 232A than the
one in the 232.  They changed resistor values or something, which
resulted in the samller capacitance needed to generate the necessary
voltages.  Thus the smaller caps needed.
BTW, on the 232, I have used 10uF caps with no apparent problems,
so I imagine there is a range of values that would be compatible.
I would guess that the recommended values are the minimum needed to
operate correctly.

                                          Regards,

                                            Jim



On Fri, 30 June 2000, "Don B. Roadman" wrote:

{Quote hidden}

spam_OUTjimTakeThisOuTspamjpes.com

2000\06\30@122719 by Alan B. Pearce

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>I also dont under stand the caps, they call for 1uF for the 232
>and .1uF for the 232A. One would think there would be a range of
>cap values, perhaps with a tradeoff curve to indicate maybe less
>ouput drive capability or something. They sure seem to have
>minimalist data sheets :)

Not quite what I was on about. If you check the 3232 data sheet you will find
that different caps are specified for single voltage working, and variable
voltage working. For variable voltage one cap is 0.1uF min, and the other three
are 0.47uF min. For operating at fixed 3 Volt, all caps are 0.1uF min. For 5
volt fixed supply, one cap is 0.047uF minimum, and the other three are 0.33uF
min. Go figure - but the way I read the data sheet, it only guarantees to swing
the output +/-6 Volts.

2000\06\30@125222 by Don B. Roadman

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On 30 Jun 2000, at 17:27, Alan B. Pearce wrote:

> >I also dont under stand the caps, they call for 1uF for the 232
> >and .1uF for the 232A. One would think there would be a range of cap
> >values, perhaps with a tradeoff curve to indicate maybe less ouput
> >drive capability or something. They sure seem to have minimalist data
> >sheets :)
>
> Not quite what I was on about. If you check the 3232 data sheet you
> will find that different caps are specified for single voltage
> working, and variable voltage working. For variable voltage one cap is
> 0.1uF min, and the other three are 0.47uF min. For operating at fixed
> 3 Volt, all caps are 0.1uF min. For 5 volt fixed supply, one cap is
> 0.047uF minimum, and the other three are 0.33uF min. Go figure - but
> the way I read the data sheet, it only guarantees to swing the output
> +/-6 Volts.
>
Thanks for the info.  I didnt look at the data for these parts, only the
232 & 232A.. It does sound weird, but probably makes sense if one
had the block diagrams or the circuit for the voltage doubler circuits.

2000\06\30@152330 by Dan Michaels

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Alan B. Pearce wrote:
>>I also dont under stand the caps, they call for 1uF for the 232
>>and .1uF for the 232A. One would think there would be a range of
>>cap values, perhaps with a tradeoff curve to indicate maybe less
>>ouput drive capability or something. They sure seem to have
>>minimalist data sheets :)
>
>Not quite what I was on about. If you check the 3232 data sheet you will find
>that different caps are specified for single voltage working, and variable
>voltage working. For variable voltage one cap is 0.1uF min, and the other three
>are 0.47uF min. For operating at fixed 3 Volt, all caps are 0.1uF min. For 5
>volt fixed supply, one cap is 0.047uF minimum, and the other three are 0.33uF
>min. Go figure - but the way I read the data sheet, it only guarantees to swing
>the output +/-6 Volts.
>

AFAIK, the "minimum" cap sizes usable are mainly determined by the
channel resistance of the switches and probably more importantly, the
frequency of the internal oscillator. If you measure it, the 232A,
using .1 uF caps, probably runs much faster than 232, using 1 uF.
I can't comment about the cap selection described above [???]

Also, these devices are simply voltage "doublers", so 5v --> +/-10v
and 3v --> +/-6v.

Lastly, larger caps will help prevent output droop. Especially,
if you try to suck some juice out of these things to run some
peripheral analog cktry, the voltage will droop considerably as
the load is increased. The older 232 is maybe a little better for
this. Neither is very good for this.

- DanM


'[PIC]: ICD RS232 at 3V'
2000\07\02@053821 by Alan B. Pearce
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>The older 232 is maybe a little better for
>this. Neither is very good for this.

The MAX3232E is described as being good for running serial mice, so it would
seem that Maxim have beefed up the converter a bit maybe. This may also explain
the capacitor selections.

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