How to switch TX, RX,RTS & CTS from an RS232 port to a tranceiver?

[Jasen Betts]

Why not?

not by themselves...

This comes from an ancient BYTE (or KILOBAUD where someone had one Ter-
minal in the living room and one other near the (South-West TC 68oo IIRC)
Computer:

one Output ------*
|
|
===
/ \
/ \
-----
|
-9 Volt |
or -/\/\/--*---------> one Input
Handshake- |
Line |
-----
\ /
\ /
===
|
|
another |
Output ----------*

that won't work. (you've got the diodes backwards)

The Resistor being about 5.6 to 10 KOhm.

seems a little high.

Bye.
Jasen

 

[Pooh Bear]

not by themselves...


that won't work. (you've got the diodes backwards)


seems a little high.

I thought so too.

I also can see some potential issues with using this if the levels involved from
the various transmitters are different. Esp if one uses gnd for '0'.

Graham

 

[Jasen Betts]

I thought so too.

I also can see some potential issues with using this if the levels involved from
the various transmitters are different. Esp if one uses gnd for '0'.

0 is typically +3-12v. DYM gnd for 1 ?

 

[John O'Flaherty]

Chris wrote:

Oh, bad english again.. babelfish comes up whith "annulling" for what I
meant.

You may want 'disabling'.

 

[David Requena]

John O'Flaherty ha escrito:

You may want 'disabling'.

Yes, that's what I meant. Thanks

 

[Holger Petersen]

Holger Petersen wrote:

This "ancient" means 1978 to 1983...

Aren't the diodes the wrong way round ?

Yess, indeed.

That might indeed work but I'm not
familiar with the quiesecnt state of the RS232 lines so played safe. It would
suffer at high data rates though.

^^^^^^^^^

Remember: ""Dumb video Terminal" about 1980 ==> ca. 9600 Baud...

That could be fixed by using some active
devices though.

Graham

Holger

PS: Sorry, I do not have that special issue in my collection. I firmly
believe in one of the articles of Steve Ciarcia's "Circuit Cellar"
from BYTE, but I cant't find it.

 

[David Requena]

Yess, indeed.

Sure?
In rs-232 the "mark" (the logical 1) is always a negative voltaje (
anywhere from +3 to +15 depending on where you lookup the info). The
"space" (logical 0) is a positive voltaje in the same range.

As it seems most rs232 equipment can cope with the space being
indicated by 0 volt. In that case I could understand how this circuit
works; with the diodes placed as drawn.

As far as I understand, seting the diodes the other way round wold
require mark being positive voltage and space 0 volt. That for sure
would not be rs232 signaling by any means.

Then... what do I know? I could be completely wrong. I expose my
reasoning only so any one can correct any missconception

David

 

[Holger Petersen]

Sure?

I have doubts as well...

The (intended) function of the circuit:

The _input_ of some RS-232 - Device is held to " minus XX" Volt by
means of a (suitable) resistor which is connected to some source
of "minus XX" Volt. Neglecting the input-current of the RS232-device.
One might use a Handshake-signal of the input-devce...

One or the other *sending* devices wil be able to pull the line
to "plus YY" Volt through the diode.

This works well IF the mentioned resistor is neither too low nor
too high. This of course depends a little on the input-current
of the receiver and the voltage.

The circuit comes from the ages of 1488/1499-Chips..!

And it works only for the 'normal' TX-Date Line, dosn't it?
Of course, funny things happen if both senders will send at
the same time

Then... what do I know? I could be completely wrong. I expose my
reasoning only so any one can correct any missconception

David

Holger

 

[Jasen Betts]

Sure?
In rs-232 the "mark" (the logical 1) is always a negative voltaje (
anywhere from +3 to +15 depending on where you lookup the info). The
"space" (logical 0) is a positive voltaje in the same range.

As it seems most rs232 equipment can cope with the space being
indicated by 0 volt. In that case I could understand how this circuit
works; with the diodes placed as drawn.

As far as I understand, seting the diodes the other way round wold
require mark being positive voltage and space 0 volt. That for sure
would not be rs232 signaling by any means.

Then... what do I know? I could be completely wrong. I expose my
reasoning only so any one can correct any missconception

David

AIUI most equipment can handle mark being 0v.

with the diodes as shown the voltage will neve get more positive than -9v