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.
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.
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Reply by Neil Cherry●March 25, 20052005-03-25
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.
--
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http://home.comcast.net/~ncherry/ (Text only)
http://hcs.sourceforge.net/ (HCS II)
http://linuxha.blogspot.com/ My HA Blog
Reply by Grant Edwards●March 25, 20052005-03-25
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.
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Reply by Elder Costa●March 25, 20052005-03-25
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.
Reply by Grant Edwards●March 25, 20052005-03-25
On 2005-03-25, Elder Costa <elder.costa@terra.com.br> wrote:
> Grant Edwards wrote:
>> You're professor doesn't know what he's talking about.
>
> Or maybe his professor meant a generic digital serial
> communication channel and he interpreted RS232. Notice he said
> "RS232 port on the 6812".
The 6812 is the same as RS-232. There's a transmit data pin
and a receive data pin. For half-duplex, you've got to use
both of them.
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Reply by Elder Costa●March 25, 20052005-03-25
ramkumar.sankar@gmail.com wrote:
> Is there any way to make the rs232 port on the 6812 to work like a half
> duplex port?
>
The question sounds like (almost) overdue homework to me. You'd better
ask for help on Google Oracle about RS-232.
First, the 6812 must have (I do not know it and did not check either) a
serial port, not a RS232 port. The serial RX and TX lines are usually
connected to drivers/receivers that convert TTL/C-MOS voltage levels to
RS232 voltage levels and vice-versa. AFAIR RS232 regards to physical
connections and voltage levels only.
RS485 (another standard) transceivers may be used in a half duplex
configuration. Still the physical media is differential, therefore
twisted pair based.
Despite it looks like "could somebody help me to do my homework" I will
give you a hint anyway: one way to achieve what you want is using a
tri-state buffer. How to connect it and the pros and cons of this
configuration, as well as better ways to do it is up to you to figure out.
Regards.
Elder.
Reply by Elder Costa●March 25, 20052005-03-25
Grant Edwards wrote:
> You're professor doesn't know what he's talking about.
Or maybe his professor meant a generic digital serial communication
channel and he interpreted RS232. Notice he said "RS232 port on the 6812".
Regards.
Reply by Rufus V. Smith●March 25, 20052005-03-25
"Grant Edwards" <grante@visi.com> wrote in message
news:1147bpjoe8pu7d9@corp.supernews.com...
> On 2005-03-25, ramkumar.sankar@gmail.com <ramkumar.sankar@gmail.com>
> wrote:
>
>> Is there any way to make the rs232 port on the 6812 to work
>> like a half duplex port?
>
> Yes: don't transmit while you're receiving.
>
LOL!
Great answer, Grant. Made my morning!
Rufus
Reply by Grant Edwards●March 25, 20052005-03-25
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".
> pWhat I am trying to do is control a device that works at
> 57600 baud rate but in Half Duplex mode. But when I was
> studying the diagrams for the device I am trying to control it
> has both a Tx and Rx wire.
Right. RS-232 data lines are not bidirectional, so if you want
to both send and receive data, you'll need both of them.
Additional handshaking lines such as RTS and CTS are often used
to control the direction of data flow. The handshaking might
also be done purely in software at the protocol level.
> If anyone could point me in the direction of a good rs232
> serial communication protocol document I would appretiate it.
For what protocol?
I would suggest reading the documentation for the device you
are attempting to control.
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