[SOLVED] Hexin serial converter NOT working

[PCminister]

hi

I bought 2

Hexin

rs232 to rs485 converter and i cant make connection through them.

i took a picture of my installation:

**broken link removed**

as you can see i want these two to convert rs232 to rs485 here and after 15 meters again covert it to rs232 again.

i use these plus OMEGA USB to RS232 converter to connect to a FATEK b1 series for programming and online monitoring. I cant connect through these WHY?

THANKS

 

[barry]

First of all, your attachment didn't make through.

There are exactly 4,193 reasons why this isn't working; a few of them are:

Your baudrates don't match
Your parity doesn't match
Noise
You don't have your handshaking signals driven (or connected) (they supply power for the device)
Your cable is incorrect
Your software is incorrect (not enabling/disabling your transmitters properly)

Have you looked at your signals with an oscilloscope? That's where I'd start.

 

[FvM]

I reviewed the converter users manual and didn't manage to find out if it's using RTS for transmitter enable (won't work without a special windows driver or prerequisites in the application software) or automatic enable as most RS485 converters. It's also not said if the converter has pull-up/pull-down resistors to force correct RS-485 idle level. I would never buy a product with this kind of vague specification.

The specific behaviour of the Fatek B1 PLC is also unclear, at worst case it won't even support half-duplex communication because it sends while receiving, which won't be a problem with RS-232 or RS-422 connection.

Why do you intend to use the double conversion RS232<> RS485<>RS232 at all?

 

[PCminister]

Your software is incorrect (not enabling/disabling your transmitters properly)

it works without converters.

Have you looked at your signals with an oscilloscope?

dont have one

Your cable is incorrect

its not.

You don't have your handshaking signals driven

how can i check that?

Your baudrates don't match
Your parity doesn't match

how can i match them?

I would never buy a product with this kind of vague specification.

its a cheap product. i just wanted to learn.

Why do you intend to use the double conversion RS232<> RS485<>RS232 at all?

i couldnt get it to work with rs232.

i test these on a DELTA SV series but couldnt connect.

dont you think that i need to supply power with an external source?

which pins should i connect power to?

 

[barry]

It didn't work with simple RS-232, so you ADDED more (and more complicated) hardware????? That's like saying, "I don't know how operate a can opener so I'll just get a nuclear reactor."

If it didn't work with RS-232, it most certainly is not going to work with RS-485. And if you don't know that the transmitter and receiver both have to be configured for the same baudrate, parity etc. then you need to educate yourself about serial communications.

You say "It worked without converters" and then you say "I couldn't get it to work with rs232". Well, which is it?

 

[PCminister]

im sorry

i didnt explain the situation well

i have a PLC and a HMI. distance between them 15 meters.

i want to monitor PLC while i see the HMI.

so i need to have the rs232 15 meters from the plc.

and in another project i need to connect PLC to HMI with rs232 (D:20m)

rs485 is just easier in long distances dont you agree?

If it didn't work with RS-232, it most certainly is not going to work with RS-485. And if you don't know that the transmitter and receiver both have to be configured for the same baudrate, parity etc. then you need to educate yourself about serial communications.

when im using OMEGA converter beside plc it works fine and in 15 meters distance it doesnt.

i know that much that buad rate and parity must match. i meant that how can i know buad rate of converter to match my usb converter with it.

i thought using rs232 to rs485 converters is a common thing.

rs232 is not as stable as rs485 in long distances right?

You say "It worked without converters" and then you say "I couldn't get it to work with rs232". Well, which is it?

when im next to plc rs232 works fine but when im 15 meters away it doesnt.

 

[FvM]

I don't know what the baus rate is, but RS232 connection may have problems with long distance and high baud rate.

For the reasons mentioned above, it's not clear if the RS-485 will work under this conditions. It's necessary to check if the HMI communication can work in half-duplex and if the RS-485 converter depends on external transmit enable control.

It would be better to use a full duplex RS-422 which transmit RS-232 signals without restrictions.

 

[PCminister]

I don't know what the baus rate is, but RS232 connection may have problems with long distance and high baud rate.

it was 9600 but i checked with 4800 and still no connection

it is half-duplex (i connected 2 wire for 485 to plc). i thought every plc is half-duplex isnt it right?

but right now my problem is these to converters. why cant i get them to work. where did i go wrong?

 

[D.A.(Tony)Stewart]

How not to use serial communication should be the title of this thread, compounding lack of understanding with lack of control with added complexity.

In the '70's we had 9600 baud all across the campus with thousand of connections of RS-232 on twisted pairs to an IBM 360. There were some crosstalk issues with large cable bundles so some wire pairs had to be hand picked. A scope is essential for learning signal integrity.

As I recall it is possible to get 1Mb/s per 10 meter length or 10kb/s in 1 km as long as there are no major noise sources nearby.

The product term is the limit for the unbalanced RS-232 on twisted pair or 10kb/s per km.

RS485 has better signal integrity and may go farther but has no hardware flow control so software flow control is used.

RS-232 can use XON/XOFF software flow control or hardware lines RTS/CTS flow control whereas data sets also use DTR/DSR and Modem also use other signals.

Links can be full or half duplex (FDX/HDX) based on integrity of signals, crosstalk and application support.

We used a variety of tools then, like breakout boxes with pins or LEDs later with jumpers to satisfy any loopback hardware missing controls.
I also had cassette recorders for 9600 Baud for downloading 6800 uCode to Emulators and burn to EPROM programmers. and also made Y cable splitters so a local terminal could monitor traffic being sent from one computer to another in either direction using diodes with negative bias on HDX flow essentially monitoring traffic in Rx+Tx onto a dumb terminal Rx line.

- - - Updated - - -

This is how one alters the Serial port settings in Windows.

USB adapters with serial ports will have software with similar controls.

 

[PCminister]

Excuse me sir if im rude but you must be very old!

cassettes remind of the Commodore 64. it was a very big deal in our country.

i gave these Converters to an expert and he told me that these are not reliable and on the 485 side it cant be connected to a PLC. i bought one of these:

**broken link removed**

this thread is not over i still cant connect to plc with these converters (Hexin) and any help would be appreciated.

thanks

 

[D.A.(Tony)Stewart]

It seems old technology on serial ports , you need to study.

First define capabilities for the end points.
Then use the simplest method. RS-485 may not needed for this short distance.

 

[FvM]

A possible reason for converter failure has been explained in post #3. Converter is requiring RTS as TX-enable signal, which is not generated by a standard Windows Comport driver and most likely not available by any means for the PLC.

As long as you don't have clear specifications of converter clarifying that it's able to generate internal TX-enable signal, I would consider it unsuitable.

I already suggested full-duplex RS-422 as an alternative, because it doesn't depend on hardware enable signals.

 

[PCminister]

if i want to use it just to convert 485 to 232 it will be fine right?

if it needs RTS then its not suitable for PLC rs485?

RS-485 may not needed for this short distance.

i used 232 but got nothing on the other end. the cable i used was Cat5e and it got 485 through.

i wanted to use 422 but its converters are more expensive. money is not an issue but learning for me was a priority.

using these converters as i was told was standard in the industry. dont you agree?

THX

 

[FvM]

using these converters as i was told was standard in the industry. dont you agree?

They surely are. If you compare the Delta IFD8500 and Hexin manual, you see what the problem is. The Delta manual gives clear intructions how to use the device for different applications, for HXSP-485D neither the requirements are clearly specified, nor the operation method (TX-enable generation) is explained.