RS232 Full Duplex to Half Duplex

Grant Edwards wrote:
> The 6812 is the same as RS-232. 
Are you sure? I do not know this microcontroller in particular but most 
of them has asynchronous serial ports that comply with TTL or C-MOS 
levels, not RS-232. Therefore I would't call them RS-232.

> There's a transmit data pin
> and a receive data pin.  For half-duplex, you've got to use
> both of them.
> 
Agreed. I think the both of us are talking about the same thing.

Regards.

Elder.

On 2005-03-25, Elder Costa <elder.costa@terra.com.br> wrote:

>> The 6812 is the same as RS-232. 

> Are you sure?

In regards to half/full duplex issue and the number/direction
of data lines.

-- 
Grant Edwards                   grante             Yow!  I love FRUIT
                                  at               PICKERS!!
                               visi.com            

On Fri, 25 Mar 2005 14:24:49 -0000, Grant Edwards wrote:
> On 2005-03-25, ramkumar.sankar@gmail.com <ramkumar.sankar@gmail.com> wrote:
> 
>> Well I am not an expert on rs232 communication, but I was told by my
>> professer that in half duplex rs232 there was only 1 wire between the
>> two devices.
> 
> You're professor doesn't know what he's talking about.  
> 
> Half duplex means that only one side transmits at a time.  Half
> duplex RS-232 links don't use just 1 wire.  They use the 2 data
> lines plus usually use RTS and CTS to control the link
> "direction".

Back in the 80's I remember wiring up a IBM 3101 terminal in the
weirdest way. The Tx & Rx were tied together (a diode on the Tx) and
1 wire was used for Tx & Rx. It was hooked up to a mainframe (not IBM)
and used for terminal access. Would that be simplex? It is half duplex
as it can only transmit in one direction at a time.

I won't claim to be an expert on RS232 just had lots of experience
with cabling up 'RS232' devices (printers, terminals, modems,
computers) and getting them to work in the weirdest ways.

-- 
Linux Home Automation         Neil Cherry       ncherry@comcast.net
http://home.comcast.net/~ncherry/               (Text only)
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http://linuxha.blogspot.com/                    My HA Blog

On 2005-03-25, Neil Cherry <njc@wolfgang.uucp> wrote:

>> Half duplex means that only one side transmits at a time.  Half
>> duplex RS-232 links don't use just 1 wire.  They use the 2 data
>> lines plus usually use RTS and CTS to control the link
>> "direction".
>
> Back in the 80's I remember wiring up a IBM 3101 terminal in the
> weirdest way. The Tx & Rx were tied together (a diode on the Tx) and
> 1 wire was used for Tx & Rx.

Not sure what that was, but it sure doesn't sound like RS-232.
If it was, the spec was being violated about six different ways.

> It was hooked up to a mainframe (not IBM) and used for
> terminal access. Would that be simplex?

Simplex means data only goes one way, so I doubt it.

> It is half duplex as it can only transmit in one direction at
> a time.

Yes.

> I won't claim to be an expert on RS232 just had lots of experience
> with cabling up 'RS232' devices (printers, terminals, modems,
> computers) and getting them to work in the weirdest ways.

I've heard of people using various kludges to hook up multiple
RS-232 drivers to a single receiver.  

-- 
Grant Edwards                   grante             Yow!  O.K.! Speak with a
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On Fri, 25 Mar 2005 17:46:24 -0000, Grant Edwards wrote:
> On 2005-03-25, Neil Cherry <njc@wolfgang.uucp> wrote:
> 
>>> Half duplex means that only one side transmits at a time.  Half
>>> duplex RS-232 links don't use just 1 wire.  They use the 2 data
>>> lines plus usually use RTS and CTS to control the link
>>> "direction".
>>
>> Back in the 80's I remember wiring up a IBM 3101 terminal in the
>> weirdest way. The Tx & Rx were tied together (a diode on the Tx) and
>> 1 wire was used for Tx & Rx.
> 
> Not sure what that was, but it sure doesn't sound like RS-232.
> If it was, the spec was being violated about six different ways.

Yeah, I knew I was walking the line on that one so I didn't mention
RS232. :-)

>> I won't claim to be an expert on RS232 just had lots of experience
>> with cabling up 'RS232' devices (printers, terminals, modems,
>> computers) and getting them to work in the weirdest ways.
> 
> I've heard of people using various kludges to hook up multiple
> RS-232 drivers to a single receiver.  

I think this was on of those kludges to put an RS232 terminal on a
multidrop line. He was probably using it as a debug terminal.

-- 
Linux Home Automation         Neil Cherry       ncherry@comcast.net
http://home.comcast.net/~ncherry/               (Text only)
http://hcs.sourceforge.net/                     (HCS II)
http://linuxha.blogspot.com/                    My HA Blog