Laptop to PIC Interface

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I have a hobby project where I would like to interface a laptop PC to a PIC
project utilizing the PC's RS-232 port.

I have the PIC software and the PC software but I'm a bit uncertain as to
the electrical interface between the two computers.  Can I use the 1488 and
1489 ICs for this interface or is there something simpler?



Re: Laptop to PIC Interface
On Fri, 01 Oct 2004 02:25:48 GMT, "Marlowe"

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Maxim MAX232 or similar parts do both RS-232->TTL and TTL->RS-232.

If you want to do it "cheap and nasty", a TTL inverter on the PIC
serial out will normally drive a PC serial port.

The usual RS-232 drivers do both a level conversion and an inversion.


--
Peter Bennett, VE7CEI  
peterbb4 (at) interchange.ubc.ca  
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Re: Laptop to PIC Interface
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The very simplest way is to invert the output of your serial port and
just connect it direct to the PC. Many (but not all) PCs will accept
an 0-5V swing.

A better way is to use a chip like the MAX232A line interface. This is
superior to the 1488/89 combo because it has its own on-chip charge
pump to generate +/-10V.

Re: Laptop to PIC Interface
On Fri, 01 Oct 2004 02:25:48 GMT, "Marlowe"

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As others have said, the MAX232-type chips are easier to use because
they need only +5 volts and they generate the +/- 9 v. voltages using
built-in charge pumps and four small capacitors that you supply.  The
1488 and 1489 type chips will also work, but they are the older
technology that required that you supply the voltages (+ and -) some
other way.  If you happen to have +12 and -12 volts available, you can
use the 1488 and 1489.  But for new designs the ones with the built-in
charge-pump are the way to go.  For strictly experimental use, you can
try using a 0 to +5 volt swing.  You will need to use inverters
between your PIC and the PC because the PIC TxD and RxD lines are
designed to be used with inverting buffers, such as the 1488/1489 or
the MAX232.  In receiving from the PC, take some steps to protect your
input circuit from the possible +/-12v swing that you could find on
the serial line from the PC.  All you need here is a one-transistor
inverting buffer with a large resistor on the base to be able to stand
the +12v, and a diode to protect the base during the -12v times.


-Robert Scott
 Ypsilanti, Michigan
(Reply through this forum, not by direct e-mail to me, as automatic reply
address is fake.)

Re: Laptop to PIC Interface
Thanks to all for suggesting the MAX232.  I downloaded the data sheet and it
is just what I need.

As an aside, I live out in the country, but I have to go into the city for a
dentist appointment Monday.  I called the electronic supply store and
inquired about whether they stocked the MAX232.  Yes they did, but the price
is $8.50 each.  I just placed an internet order with Mouser Electronics for
$1.05 each for the IN version!


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PIC
and
address is fake.)



Re: Laptop to PIC Interface
On Fri, 01 Oct 2004 20:17:04 GMT, "Marlowe"

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Also, I think Texas Instruments has a pin-compatible MAX232
equivalent.


-Robert Scott
 Ypsilanti, Michigan
(Reply through this forum, not by direct e-mail to me, as automatic reply
address is fake.)

Re: Laptop to PIC Interface
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   There are lots of second sources.  The retailer nearest
our shop stocks (Hylink?)  HY232 at CAN$2 each.  When I
looked to double check this, I see the board in front of me
used an Analog Devices ADM232 instead.

        Regards.        Mel.

Re: Laptop to PIC Interface
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You can get closer to proper specs by using an op-amp with +5/-5V
supplies.  You can even build in a little bit of hysteresis and
adjust the trip point.

--
Chuck F ( snipped-for-privacy@yahoo.com) ( snipped-for-privacy@worldnet.att.net)
   Available for consulting/temporary embedded and systems.
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Re: Laptop to PIC Interface
An interesting alternative to the MAX232 family that I've used many times
with excellent results is the DS276. Although with somehow limited
capabilities (e.g. 20 kbps max.
data rate, only one transceiver per package, not fully compliant with the
RS232 norm),
this thing has been designed for battery-powered systems.
The transmitter steals power from the receive signal line to save power. A
single 8-pin chip without any external components is frequently all you need
to implement a serial interface that consumes very little power. It is also
very cheap.

-LENS

Life is not measured by the breaths you take, but by the moments that take
your breath away...



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PIC
and
address is fake.)



Re: Laptop to PIC Interface
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Please don't toppost.

Put two in communication with each other and you have a perpetual
motion machine :-)

--
Chuck F ( snipped-for-privacy@yahoo.com) ( snipped-for-privacy@worldnet.att.net)
   Available for consulting/temporary embedded and systems.
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