RS 232 to RS 485 converter

Check your UART bits and baud rates and try again.

Don't forget to check the handshake pins or setting(on both sides of the link.

Look at baud rate setting,baud rate, number of bits in data, parity bit, stop bit, hand shaking option hardware/software/none, and finally link of signals RxD, TxD RTS CTS, etc. You can even take help of the PLC supplier who can send proper cable to you. They can also give you right catalog to refer.

Having done this a few times over the years, I know it can be a bit difficult, even for someone who cut their teeth on such things.

You need at least an RS232 breakout box with LEDs to show you what is going on at least on the RS232 side....

Look here for a really cheapo version:-

http://www.altex.com/RS232-Breakout-Box-BRB-232-P140389.aspx

Usually they cost a lot more. Search on "RS232 Breakout", you will find dozens of them.

You need to know exactly the baud rate, start bits, stop bits etc... to even have a chance of getting it to work...from BOTH sides......

Here is the details of the RS485 side:-

http://en.wikibooks.org/wiki/Serial_Programming/RS-485

And here is the deatails of the RS232 side:-

http://en.wikibooks.org/wiki/Serial_Programming/RS-232_Connections

Best of luck.....

I went through this once or twice at a customers facility, it always ended up being the cheap three wire RS232 cables they sell these days...

...which will only work using X-on and X-Off protocol!!

There is no convention or standard for the half duplex (2 wire) RS-485 lines, A or B, or (+) or (-).

Some divisions of large conglomerates label the lines one way, another division labels them the exact opposite.

So, if you're running half duplex (2 wire), then try it with the 2 wires attached one way, if that doesn't work, try it the other way. Reversing the wires will not damage the drivers/receivers on either side, but it won't work 'backwards'.

You are correct...having been in the video/data/audio transmission game for a while now, we often get customer 'complaints' that our modems don't work only to discover that the 2-wire connections need to be swapped. As there is (as you rightly point out) no clear convention and the confusion of input/output with respect to the computer and/or modem, we state in our manuals that if there is no communication to try and swap the +/- wiring on one or both ends. This usually sorts out the problem.

1. RS232 did not use cables with send to receive cross-over...
2. RS232 was designed to connect a Data Terminal Equipment [DTE] - typically a computer - to a Data Communication Equipment [DCE] - typically a modem.
3. It was a bad standard - it did not specify if connectors were to be male or female on a type DCE or DTE. To compound matters, the signal codes labels were from the DTE's "point of view" at both ends e.g. TD is data out at DTE end, but at DCE end the same pin number (still labelled TD) is really an input!
   
4. If you connect a DTE with a DCE using a "standard" RS232 cable, with 9 pin connectors (The original standard had 25 pin connectors, because it includes a secondary channel for management communication - the 9 pin became a standard because IBM used it on later "IBM PCs") the cable connects pin 1 of connector A to pin 1 of connector B, pin 2 to pin 2, and so on until pin 9 connects to pin 9.
5. But if both ends of your link are wired as DTE (both PLC and computer can consider themselves as computers) , you have input connected to input and output connected to output. There is no communication!
6. There are two basic types of RS232 cable, normal (DTE to DCE) and crossover or DCE/DCE). Plus variants which "fix" the "handshake" signals so that the sending side always gets "OK to send" input....
7. It appears you have got a physical connection! Often one finds that the connector on the lead you have is the wrong gender to fit the equipment at one or both ends! Or even 25 pin, when you expected 9 pin.
8. The first thing to do is to check if the "RS232" cable is wired pin 2 at one end to pin 2 at the other connector.
   
9. The next thing to do is find what sort of termination the PLC thinks it is. DTE or PLC. Refer to the PLC data. Since suppliers have a vested interest in selling you their lead, this is often not clear or just not mentioned.
10. Sorry to tell you that, to cope with just one PLC, computer and modem; I had a whole bag of male-female converters (9 and 25 pin), straight and cross-over cables and an LED signal indicator to check which pins were giving an output.

Following diagram from my design notes may help to get you started. Note computer end was DTE, while ICM200 [an RS232 to RS422 signal standard converter] was DCE :-

a) CABLE HAS 9 PIN "D" TYPE CONNECTOR (slidelock)
FEMALE AT ICM200 END & FEMALE AT COMPUTER END.

b) CABLE PIN INTERCONNECTION REQD IS:-

ICM200 Computer direction function
pin pin
RD 2 >------------------------------<2 from ICM200 RD data
TD 3 >------------------------------<3 to ICM200 TD data
RTS 7 >------------------------------<7 to ICM200 RTS handshake
CTS 8 >------------------------------<8 from ICM200 CTS handshake
com 5 >------------------------------<5 - signal common
DSR 6 >------------------------------<6 from ICM200 DSR handshake
DTR 4 >------------------------------<4 to ICM200 DTR handshake
DCD 1 >------------------------------<1 from ICM200 DCD handshake
NC 9 >------------------------------<9 to computer RI (ring)

N.B. NC= no connection.

- you will probably note how much detail was essential to get the right connection!!

Dear Niranjan,

Further to my post about RS232 "Standard", there is another point which may be relevant.

1. RS232 connectors do not have any power output pins, only signal pins. Nor do RS485 - but often PLC "Programmer" connectors have power pins on their RS422 or RS485 connectors.
2. Often, RS232 interfaces "steal" the [very limited] power from the signal outputs to power conversion circuits. The better ones have an independent power supply
3. This "power steal" (2.) may work OK on a short cable with an RS485 end which does NOT have a termination resistor [usually 120 ohms] built-in. But it may be incapable of enough drive output at the RS485 side.
   
4. You must check, with a meter, at the two ends of your "RS232" cable, to find which pins give an output voltage - this will tell you if they are DTE or DCE.

Best of luck....

67model

If the OP bought an RS232 - RS485 converter then i don't think the issue is on the RS232 side. I believe the problem is on the RS485 connections. See Carl E's post earlier...try swapping the +/- data lines on one end first, then the other if it still does not work.

What program are you using? Details on the laptop?

A simple standard RS232 to RS485 converter only has three wires D-, D+ and Ground on the RS485 side and TX/RX on the RS232 which are required, so it shouldn't be too difficult. The most common mistake is that thebaud rate is not matching, or some of your other data settings. However also check if any of the handshake wires on the RS232 are required for your particular application.

A simpler way may be using a USB to RS-485 converter. We have drivers for Windows 7 32 and 64 bit also. Most laptop computers do not come with RS-485 or RS-232 ports. Our I-7561 provides solutions for both.

http://www.icpdas-usa.com/products.php?PID=506