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PICList Thread
'PIC to RS232'
1994\12\14@142912 by crocontroller discussion list

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>        1) Does anyone know of a good single chip solution to convert PIC
>outputs to RS232?  I am using a PIC for the diagnostics in my "Muscle
>Wire" design and I will send diagnostics data to my PC serial port.
>
>        2) I notice that Parallax calls for a MAX232 chip in their app notes
>but they don't say who makes it.  Does anyone know who makes the MAX232?


Martin, the MAX232 requires 4 caps, someone said the MAX231 requires 2 caps,
but you should really check out the MAX233.  It requires _no_ capacitors and
generates the voltages internally.


Just checked my Digi-Key catalog [(800) DIGI-KEY]:

MAX231 (+12 & + 5v powered) 2 xmitters, 2 xceivers, 14-Pin   $2.94
MAX232 (+5v pwr only) 2 xmitters, 2xceivers, 16-pin          $2.94
MAX233 (+5v pwr, no ext caps) 2 xmit, 2 xceive, 18-pin       $6.50


Then there are others that are just xmitters, etc.  So, with the 231 it
looks like you have to supply the +12v (but no -12...), with the 232 you
just supply the +5 and more caps, and with the 233 (at a price) just the +5
and no external components.

Good luck.

- JohnR

--
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Millennium Research
(408) 269-1814 vox
(408) 269-9323 fax

1994\12\14@200956 by crocontroller discussion list

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About RS232-to-PIC communications,

I'm a total novice when it comes to analog circuitry, so this probably isn't
the most elegant of solutions.

I needed a simple, robust, low-power RS232 connection for my data logger. I
minimised the components on the logger by using an "active" plug. It works
like this:

The logger itself has only two connections: GROUND and DATA. DATA goes
straight to a PORT-B pin on the PIC through a resistor.

The plug contains an op-amp (eg 741) powered from the DTR and RTS pins via
diodes (for protection). One input of the 741 sees a voltage of around 0.6
volts (actually, one diode-drop above ground). The other input is connected
to DATA. Receive (from the host) is connected to DATA via a resistor. Transmit
(to the host) is connected to the ouput of the OP-AMP. You can fit the whole
arrangement (OP-AMP + a few diodes) in a 9-pin backshell.

Advantages are:
(1) No active components on the PIC board. All power is drawn from the host.
(2) The output of the OP-AMP swings to the supply voltages, so you get whatever
output voltage range the host uses (+-5v, +-12v, etc.) minus about 0.6v.
(3) Only 2 wires connect to the PIC. For a logger like mine this is a definite
plus. You can put the PIC inside a canister and communicate through the casing
(arranged like a lithium cell) - no sockets required.

Disadvantages are:
(1) The link is half-duplex. Every character sent by the host is echoed by
the interface.
(2) You need to be able to control the handshaking lines to some extent. On a
PC this is no problem.
(3) Its a little wierd, but sometimes wierd is the only way to go.

Hope this helps someone out there...

Stewart Smith
.....ssmithKILLspamspam@spam@csuvax1.murdoch.edu.au

1994\12\16@170949 by crocontroller discussion list

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I have used a 74HC14 with a 10K resistor on the input as a RS-232 receiver
transmitter.  Although it is a little bigger than a 741, it uses less power
(essentially zero except when data transfers).  The only problem I know of
with this scheme is if the serial receiver at the other end needs to see a
negative voltage for a mark condition.  The 1489 receiver doesn't, the TI
receiver chip that's used for RS-232 does.  I don't know about MAX chips,
etc.  It does work quite nicely though and I still have 4 inverters left
over.


'pic to rs232'
1999\04\16@150105 by Julian Fine
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Has anyone used a pic and a RS232 chip to talk to a modem using standart at
commands.

************* Julian Fine ***********
********** julianspamKILLspamfine.co.za *********
******* http://www.fine.co.za *********

1999\04\16@161324 by Gerhard Fiedler
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At 20:17 04/16/99 +0200, Julian Fine wrote:
>Has anyone used a pic and a RS232 chip to talk to a modem using standart at
>commands.

i haven't used a pic, but i've written other serial comm applications --
the modem part is the same, it's a layer above the serial communications.
once your rs232 rx and tx works, you run the modem commands on them. if you
need help with that, just ask.

ge

1999\04\19@011140 by Tjaart van der Walt

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Julian Fine wrote:
>
> Has anyone used a pic and a RS232 chip to talk to a modem using standart at
> commands.

Not a standard modem, but I've been playing with GSM modems
for a little while (hehehe) now, so you are welcome to ask
me if you like...

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1999\04\19@105026 by mdelong

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Ok....I'll bite, could you tell us about it?

Regards,

Mike DeLong

Tjaart van der Walt wrote:

> Julian Fine wrote:
> >
> > Has anyone used a pic and a RS232 chip to talk to a modem using standart at
> > commands.
>
> Not a standard modem, but I've been playing with GSM modems
> for a little while (hehehe) now, so you are welcome to ask
> me if you like...
>

1999\04\19@110929 by Tjaart van der Walt

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"Bancherd(Mike) DeLong" wrote:
>
> Ok....I'll bite, could you tell us about it?
>
> Regards,
>
> Mike DeLong

It works exactly like a 'normal' hayes modem, except it
has a few extra commands that enable you to interact with
the GSM network, or to get the status of the network.

You can also send and receive SMS messages (140 bytes,
or 160 chars).

It is quite possible to handle such a modem with a PIC.
In fact, I have been doing it for the past 2.5 years.
I was being a smartypants with Julian, because he knows
I've been playing with them. (Hi Jules!)

--
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|--------------------------------------------------|
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|R&D Engineer : GSM peripheral services development|
|--------------------------------------------------|
| Mobile : @spam@tjaartKILLspamspamsms.wasp.co.za  (160 text chars) |
|     http://www.wasp.co.za/~tjaart/index.html     |
|Voice: +27-(0)11-622-8686  Fax: +27-(0)11-622-8973|
|          WGS-84 : 26¡10.52'S 28¡06.19'E          |
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