RS232 programming and IC

Archiver

Hello

I'm not sure if anyone ever mentioned this,

but dont the basic stamps and 8051 microcontrollers
need RS232 or RS233 TTL-serial converters?

And yes this might be off subjects. Also which
microcontroller would you suggest - in terms of price
and scalability - I dont think basic stamp is the
right solution for any intermediate task

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Archiver

The answer is yes and no.

To meet the spec, RS232 should be at least +/- 5V (and sometime +/-12).
However, most modern receivers will accept 0 and 5V so you can feed
inverted data directly to most devices (but it isn't assured that it
will work).

On the reception side, you can use a 22K resistor to limit current and
depend on the Stamp's (PIC's) input protection diodes to bleed the
excess voltage. If you get -11.3V across the 22K (-12 clamped to -0.7)
you draw 500uA (less on the other excursion). So that is usually pretty
safe although some purists argue you should not use the input protection
diodes in that way.

However, if you want to "meet the spec" and enjoy improved noise
immunity and other features, you want a line driver/receiver. In the old
days we used the 1488/1489 pair, but they require +/- 12V. These are
hardly used now (I smiled to see Radio Shack closing them out for
pennies the other day). There are more modern solutions such as the
MAX232 which operate from a single 5V supply (see
http://www.al-williams.com/rs1.htm for a handy way to work with the
MAX).

Hope that helps.

Regards,

Al Williams
AWC
* New kits: http://www.al-williams.com/kits.htm




>

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Original Message

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> From: Boulat Khamitov [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=iXBSq0VXacgXv_dF3hNg_IycxvCWvcEPmMsfWM696h1TvZDL6YacGkiD1-LH9o4oSadFmZ3Srdm-uKI]boulat_usa@y...[/url
> Sent: Wednesday, March 05, 2003 4:57 PM
> To: basicstamps@yahoogroups.com
> Subject: RE: [noparse][[/noparse]basicstamps] RS232 programming and IC
>
>
> Hello
>
> I'm not sure if anyone ever mentioned this,
>
> but dont the basic stamps and 8051 microcontrollers
> need RS232 or RS233 TTL-serial converters?
>
> And yes this might be off subjects. Also which microcontroller would
> you suggest - in terms of price and scalability - I dont think basic
> stamp is the right solution for any intermediate task
>
> __________________________________________________
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