RS422 to RS232 converter.

[HellasTechn]

Good day !

I have been searching the net for some cheap RS422 to RS232 converter. While i have found tons of RS232 to RS422 converters, i have found none to do the opposite.

Anyone have an idea where i can find one or a circuit diagram i could use to build one ?

Thank You !

 

[kellys_eye]

There isn't one because you'd have to 'choke' the RS422 signal (10Mb/s) back to under 1Mb/s for the RS232 to work. Not to mention the multi-drop facility.....

If you wanted one I suspect you'd have to use opto-couplers to maintain the system balance and the opto-couplers outputs simply switch at RS232 levels (real or 'fake') with a ground reference.

 

[HellasTechn]

What do you mean switch ar rs232 levels ? could you explain more please ? or could you make a diagram ?

 

[HellasTechn]

Here i should say that i can use either TTL level rs232 like the one used by UART or hardware rs232 signals that are then converted to TTL level with the transistor inverter circuit.

 

[kellys_eye]

What do you mean switch ar rs232 levels ?

you answered yourself....

Here i should say that i can use either TTL level rs232 like the one used by UART or hardware rs232 signals

'True' RS232 uses a ± supply (generally 12V) but that's quite rare these days - note the legacy -12V supply line on some PC power supplies - but TTL level is more prevalent now.

 

[Minder]

I built one for for converting bi directional RS244-RS232 to a Mitsubishi PLC, it is based on the Beijer cable version, The IC's used are a couple of 75179 and a MAX202.
M.

 

[HellasTechn]

after searching i came across this
http://www.bb-elec.com/Learning-Cen...es-for-Differential-Pair-Signals-(RS-422.aspx

judging by the picture i would say that the rs422 B line is identical to the rs232 TTL line.

could i cust use the B line ground referenced ? or maybe with a forward biased signal didoe like 1n4148 in series to block potential negative voltages ?

could it be that simple ?

 

[Minder]

The Beijer one no good? 3 ic's
M.

 

[dorke]

Well,
Apart of the powering issue these devices are bidirectional!
i.e they perform both ways, so they are basically doing 2 ways conversions.

1. Use an externally powered device.
2. Think about the RS-422 termination issue.
3. Like Kelly said,assumption of low enough baud rate to be comparable with both standards.

 

[Minder]

Just use half the circuit if only one direction needed!
Worked for me.
M.

 

[HellasTechn]

The Beijer one no good? 3 ic's
M.

Iam not sure... i can not read the picture. its too small.

Well,
Apart of the powering issue these devices are bidirectional!
i.e they perform both ways, so they are basically doing 2 ways conversions.

I dont understand the bi directional.

 

[HellasTechn]

OK. i have an rs232 transmitter and an rs232receiver. The receiver is not supposed to send anything back to the transmitter. Only "listen"...

 

[dorke]

Is this for the same last project that was uploaded here?
Why do you need RS-422?
It is(was) usually used for long distance,high speed (relative to RS-232).

 

[Minder]

Iam not sure... i can not read the picture. its too small.
.

I will see if i can find my own print I made,
M.

 

[Minder]

This show it a little clearer, you may be able to adapt it.
The 4 IC's on the left are 2 75179b, the one on the right is a MAX202.
Half way down.
http://forums.mrplc.com/index.php?/profile/52109-akahige/&do=content&type=forums_topic_post&page=2
M

 

[HellasTechn]

Is this for the same last project that was uploaded here?
Why do you need RS-422?
It is(was) usually used for long distance,high speed (relative to RS-232).

The concept is the same but the project is different.

I had an rs232 transmitter that i needed converted to TTL to supply a Microcontroller.
Now i have an rs422 transmitter that i need to convert it to TTL to supply the same type microcontroller. Only in this case the problem is that the Microcontroller only supports 2 wire comm (data and gnd like the rs232).

 

[HellasTechn]

This show it a little clearer, you may be able to adapt it.
The 4 IC's on the left are 2 75179b, the one on the right is a MAX202.
Half way down.
http://forums.mrplc.com/index.php?/profile/52109-akahige/&do=content&type=forums_topic_post&page=2
M

My concern is that since i need TTL signals in the first place then why not just use the signal on line B instead of building the circuit that will give me a -5V to +5v rs232 ?

First chance i get, i will use the Oscope and check the rs422 lines to see if they really are as shown in the picture and then if they are... i will try to beed line B to the microcontroller to see if it can read it.

 

[dorke]

In this case (listen only).
Use a receiver IC like the AM26C32 ,MC3486 or DS3486 ,you actually need a single receiver (of the 4 in the IC).
There are also dual receiver ICs like the uA/MC9637
These are ICs requiring a single +5v p.s for operation.

Using a single line(unbalanced, like RS-423) is possible,but highly not recommended !
You can not directly connect it to TTL!
In any case you should have a dedicated receiver to translate the levels.

If the output is RS-422 it should have a spec. defining the speed,range etc.
Using an unbalanced receiver will limit the range and speed possible,
as well as noise immunity and ESD capability.

The receiver end should have a termination resistor.
Typically a single 100 ohm at the furthest receiver point.

In any case you should use 2 wires(422 or 423).

What is the operating speed?
What is the range?
How many receivers listening on the line?

 

[HellasTechn]

There are also dual receiver ICs like the uA/MC9637

Do they provide rs232 (-12V - +12V) ? or TTL (0V - +5V) ?

Using a single line(unbalanced, like RS-423) is possible,but highly not recommended !
You can not directly connect it to TTL!
In any case you should have a dedicated receiver to translate the levels.

I understand...

If the output is RS-422 it should have a spec. defining the speed,range etc.

I am not sure.

What is the operating speed?

4800 BPS

What is the range?

about 30 meters.

How many receivers listening on the line?

one rs422 and one rs232 (microcontroller).

I think i should have provided the diagram in post 1. Sorry !


In the diagram below, the red line is what i was thinking to try.

P.S.
The microcontroller will use two different inputs to read each transmitter and only write to the LCD. The rs422 receiver has two different inputs, will "listen only" and will not send back anything to the transmitters.

There is really nothing more than that. in other words the receivers work
independently and use the transmitter only to obtain certain information.

 

[dorke]

You have low speed and short distance.
But,
Actually you have 2 transmitters feeding 2 receivers .
Is the uC for just monitoring the the "working line"?

The ICs would be perfect for you,you can get one for about 1$.

Place them on the uC board power them with 5V.
They provide TTL level signals at their output to be used by the uC.
You will gain nothing by working un-balanced,stick to the balanced RS-422.