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In article <476c4i$op9@news.dmpe.CSIRO.AU>, m.ballard@chem.csiro.au (Mat Ballard) writes...
>hi there !
> 
>i'd appreciate any help or pointers on how to do the following.
> 
>i need to switch an individual serial port line on and off: ie:
>make pin #1 +5V, and pins #2 - #37 0V.

Assuming standard wiring on a DB-25 connector, pin 1 is frame ground, so you
can't make it +5!

If you can direcly

Peter Bennett VE7CEI                | Vessels shall be deemed to be in sight
Internet: bennett@triumf.ca         | of one another only when one can be
Packet: ve7cei@ve7kit.#vanc.bc.ca   | observed visually from the other
TRIUMF, Vancouver, B.C., Canada     |                          ColRegs 3(k)
GPS and NMEA info and programs: ftp://sundae.triumf.ca/pub/peter/index.html

In article <476c4i$op9@news.dmpe.CSIRO.AU>, m.ballard@chem.csiro.au (Mat Ballard) writes...
>hi there !
> 
>i'd appreciate any help or pointers on how to do the following.
> 
>i need to switch an individual serial port line on and off: ie:
>make pin #1 +5V, and pins #2 - #37 0V.

The usual serial port connector is only 25 pins, and 9 pin connectors are not
uncommon - are you _really_ referring to a serial port??

Pin 1 on a DB-25 is protective ground, you had better not be able to make it
+5V!

You will have no direct control of the serial data lines, pin 2 or 3.  There
are a few controllable pins, if you can write directly to the UART control
register, but the levels will be either +12 or -12 - not 0 or +5.


Peter Bennett VE7CEI                | Vessels shall be deemed to be in sight
Internet: bennett@triumf.ca         | of one another only when one can be
Packet: ve7cei@ve7kit.#vanc.bc.ca   | observed visually from the other
TRIUMF, Vancouver, B.C., Canada     |                          ColRegs 3(k)
GPS and NMEA info and programs: ftp://sundae.triumf.ca/pub/peter/index.html

In article <31OCT199522341928@erich.triumf.ca> bennett@erich.triumf.ca (P.Bennett) writes:
>
>You will have no direct control of the serial data lines, pin 2 or 3.  There
>are a few controllable pins, if you can write directly to the UART control
>register, but the levels will be either +12 or -12 - not 0 or +5.

Is this the case on a PC? I know the RS232 *used* to be +/-12V, and the
RS423 was introduced as a +/-5V version, but I thought RS232 these days was
also +/-5V? Certainly (as I believe I have mentioned in this group before
:-)) I can connect my PC's RS232 to my BBC's RS423 with no (apparent)
problem (yet...)
-- 
============================================================================
| David Burbridge (d.burbridge@ic.ac.uk) | Change is inevitable...         |
| Mech Eng Dept, Imperial College, London|  except from a vending machine! |
============================================================================

In article <477k6r$b8q@oban.cc.ic.ac.uk>, djbur@ic.ac.uk (Mr D.J. Burbridge) writes...
>In article <31OCT199522341928@erich.triumf.ca> bennett@erich.triumf.ca (P.Bennett) writes:
>>
>>You will have no direct control of the serial data lines, pin 2 or 3.  There
>>are a few controllable pins, if you can write directly to the UART control
>>register, but the levels will be either +12 or -12 - not 0 or +5.
> 
>Is this the case on a PC? I know the RS232 *used* to be +/-12V, and the
>RS423 was introduced as a +/-5V version, but I thought RS232 these days was
>also +/-5V? Certainly (as I believe I have mentioned in this group before
>:-)) I can connect my PC's RS232 to my BBC's RS423 with no (apparent)
>problem (yet...)

I think the RS-232 spec calls for voltages between 5 and 15 volts, or so, but
most receiver circuits actually have a threshold of +1 volt or so, so the
driver doesn't have to actually go negative - a 0 - +5 input will usually work.

Peter Bennett VE7CEI                | Vessels shall be deemed to be in sight
Internet: bennett@triumf.ca         | of one another only when one can be
Packet: ve7cei@ve7kit.#vanc.bc.ca   | observed visually from the other
TRIUMF, Vancouver, B.C., Canada     |                          ColRegs 3(k)
GPS and NMEA info and programs: ftp://sundae.triumf.ca/pub/peter/index.html

In article <31OCT199522255095@erich.triumf.ca>,
   bennett@erich.triumf.ca (P.Bennett) wrote:
>In article <476c4i$op9@news.dmpe.CSIRO.AU>, m.ballard@chem.csiro.au (Mat 
Ballard) writes...
>>hi there !
>> 
>>i'd appreciate any help or pointers on how to do the following.
>> 
>>i need to switch an individual serial port line on and off: ie:
>>make pin #1 +5V, and pins #2 - #37 0V.
>
>Assuming standard wiring on a DB-25 connector, pin 1 is frame ground, so you
>can't make it +5!
>
>If you can direcly
>
>Peter Bennett VE7CEI                | Vessels shall be deemed to be in sight
>Internet: bennett@triumf.ca         | of one another only when one can be
>Packet: ve7cei@ve7kit.#vanc.bc.ca   | observed visually from the other
>TRIUMF, Vancouver, B.C., Canada     |                          ColRegs 3(k)
>GPS and NMEA info and programs: ftp://sundae.triumf.ca/pub/peter/index.html

I'd be happy to know where to find pin 37 on a DB-25 connector.

Bill

In article <47bibk$24c@news.gate.net> bhutto@gate.net (William Hutto) writes:
>In article <31OCT199522255095@erich.triumf.ca>,
>   bennett@erich.triumf.ca (P.Bennett) wrote:
>>In article <476c4i$op9@news.dmpe.CSIRO.AU>, m.ballard@chem.csiro.au (Mat 
>Ballard) writes...
>>>hi there !
>>> 
>>>i'd appreciate any help or pointers on how to do the following.
>>> 
>>>i need to switch an individual serial port line on and off: ie:
>>>make pin #1 +5V, and pins #2 - #37 0V.
>>
>>Assuming standard wiring on a DB-25 connector, pin 1 is frame ground, so you
>>can't make it +5!
>>
>>If you can direcly
>>
>>Peter Bennett VE7CEI                | Vessels shall be deemed to be in sight
>>Internet: bennett@triumf.ca         | of one another only when one can be
>>Packet: ve7cei@ve7kit.#vanc.bc.ca   | observed visually from the other
>>TRIUMF, Vancouver, B.C., Canada     |                          ColRegs 3(k)
>>GPS and NMEA info and programs: ftp://sundae.triumf.ca/pub/peter/index.html
>
>I'd be happy to know where to find pin 37 on a DB-25 connector.

At the other end? :-)
-- 
============================================================================
| David Burbridge (d.burbridge@ic.ac.uk) | Change is inevitable...         |
| Mech Eng Dept, Imperial College, London|  except from a vending machine! |
============================================================================

m.ballard@chem.csiro.au (Mat Ballard) wrote:
>i need to switch an individual serial port line on and off: ie:
>make pin #1 +5V, and pins #2 - #37 0V.

Did anyone have a sensible answer to this question - or was everyone
too busy pulling apart the semantics of his question.

This type of serial port control is important for device control, and
some people might actually be interested in a serious answer.

Regards,
Rod

Rod Sherwin (cypher@internetnorth.com.au) wrote:
> m.ballard@chem.csiro.au (Mat Ballard) wrote:
> >i need to switch an individual serial port line on and off: ie:
> >make pin #1 +5V, and pins #2 - #37 0V.

> Did anyone have a sensible answer to this question - or was everyone
> too busy pulling apart the semantics of his question.

Well you have to admit it was pretty funny.  I got a good laugh out of it,
or at least the replies.

The serial port does not put out +5v, the RS-232 lines run between +/- 10
to 15v I think.  But you can use a chip like the MAX232 to bring the rs232
levels down to logic (0 and +5) levels.  There is another version called
the MAX233 (I think that is the #) that requires no external components,
and is a few $ more (diff of $3 for 232 and $6 or so for 233).  
 
Far better method however would be to just use the parallel port, which
outputs TTL level signals and also has TTL input so doesn't need any glue
chips, unless you plan on driving something in which case you could hook
up the appropriate chip or transistor (I always use Darlingtons).  But if
your just going to interface to another IC then just hook right to it.
Simple port I/O commands like INP and OUT in BASIC can be used to read and
write to the parallel port, and you can turn off and on whichever bits
you want quite easily.  Note you can also use INP and OUT with the serial
port as well, and turn on bits like DTR and RTS, but you don't have nearly
as many as you do on the parallel port and as stated before you would have
to run them thru a rs232-to-logic level ic anyways in order to use them as
per the initial example.   

> This type of serial port control is important for device control, and 
> some people might actually be interested in a serious answer. 

It is, and when I first was doing interfacing thought of the serial port
as well since it was all I really knew.  But now that I know better I
always think of the parallel port first, next game port and last serial
port unless its already an rs232 device.       Eric