MAX232's suitable for RS-232?

g159 · Guest

Hi guys,

I am trying to convert TTL signals from the PIC to RS-232 levels. I have a MAX232N chip from TI and the output is +-8.5V. I thought that RS-232 was supposed to be+-12 V, though. Or is this not the universal standard for everything? Can i still use the max232n for something like rs-232 communication with a PC?

Thanks a lot guys.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Yes, you can use it with a PIC.

The voltage levels are OK.
See the following section in the link below. Scroll down a little to see it.

g159 · Guest

Ok, thanks for the link to that site, I see that anything from 3-25 V can be used.

Say the PC i want to communicate with is outputting +-12 V signals. So even then, the fact that only +-8.5 V is coming out of the MAX232 will not "interfere" or "confuse" the PC then, since it expects 12V?

Thanks again-

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

The PC does not expect +/- 12v. Anything over +/- 3v will be
acceptable, according to the spec. To allow for voltage drop over
distance in the wires, and for a noise margin, the drivers put out a
higher voltage than the minimum requirement.

Use the MAX232N. Just plug it in, connect it up according to the
schematic, and go.

BLL · Joined: 11 Nov 2006 Posts: 181 Location: Birmingham, UK

Why not use the MAX233 - no external capacitors needed so PCB space is saved? Samples available even!!

Brian

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

dbotkin · Joined: 08 Sep 2003 Posts: 197 Location: Omaha NE USA

The *spec* says +/- 3V or better. If you take a look at the actual requirements of every RS/EIA-232 line receiver since dinosaurs roamed the Earth and ICs had ceramic packages, I have yet to find any that actually *required* a negative voltage. Ever. In fact, the guts almost always have a clamp diode to whack any negative voltage.

Check http://www.botkin.org/dale/rs232_interface.htm (or the latest ARRL Handbook)if you want to see a dead simple, dirt cheap interface that has so far worked with anything I've connected it to. It's also worked with anything many hundreds of users have connected it to. It's what I have been using for a couple years now on my ID-O-Matic kit, and so far no one has yet come up with anything it won't talk to. In small lot quantities it will cost you less than $.20 and take up less board space than a MAX-2xxx device.

You're welcome. Smile