RS232 Data Transmission Problem

Do you have another PC you could try, or even a (good quality) USB/RS232 adapter? Sometimes the output from an RS232 port will work in many applications, but isn't up to full spec., and will fail (intermittently) in other applications.

I have tried another pc, problem don"t go. I ll check with a another possibly good quality USB/RS232 adapter.

Thanks for quick reply.

I'll second the oscilloscope, as what I consider the most important piece of test gear. A DSO would be handy.

What Baud rate are you using? Is the system totally broken? Check that both ends have the same Baud settings. Check that parity is the same, as well stop bit length.

Look at the signal (TX and RX) with the O'scope, make sure the edges are not mushy. But if they start getting faster then a few microseconds your transmission line effects can induce 'reflection' noise.

The O'scope will tell you everything about the signal integrity. If you can, use another program to send out an AA or 55 hex pattern, and verify you can see this on the O'scope.

Did the ground wire get broken in the cable. Did a ground wire of the CNC mill break inducing noise in the RS232 system? Even though you are indicating opto couplers, ground noise can upset the RS232 transmission.

A cable fault can sometimes escape the multimeter test. Try another cable before messing with possibly good boards. Then check for functionality any dip switches and/or jumpers. Next, before going to component level, check local power supply rails for noise etc with an oscilloscope with the circuits on line. Next, if you don't have a scope with dedicated RS232 decoding, use a plain digital scope with enough memory in one-shot mode to evaluate the shape of the pulsestream at both Rx and Tx and decide from there. With just a multimeter I'm affraid you will not be able to troubleshoot a serial connection effectively. And do check for conflicts with any PC buld in serial ports. If you don't need them, disable them in bios. S.M.

Welcome back, Rakesh!

I remember you. I left too but came back, mostly to get my fair share of abuse.

Can you get your hands on a Breakout Box (with indicator lights)? They are very useful for troubleshooting serial interface problems.

https://www.google.com/search?q=breakout+box+rs232+serial&es_sm=122&tbm=isch&tbo=u&source=univ&sa=X&ei=EX5mU_q-JeOU8QGA0oD4Aw&ved=0CEAQsAQ&biw=1151&bih=581

Good idea.

To the OP:-

Finding RS232 problems needs a lot of knowledge, a lot of luck, or some expensive test equipment..... Mostly a bit of all three!!!

I used to have (many years ago!) a special breakout PCB with a connection for a separate PC/Laptop, where the data from both directions was shown on its screen. It made life far easier.......then it was an expensive bit of kit, including software, probably far cheaper nowadays.....

I haven't used this one myself, but it appears to be what you are looking for, for free. I leave he checking out up to you, but it was not the only one I found on the web, so look further if it isn't what you need. Seach using something like "serial sniffer" or "serial monitor" :-

http://www.serialmon.com/

Hardware you will need something like this I expect, but the downloads from that link should help better.

Best of luck:-

Some of the better USB to RS:232 adapters have status lights of RX and TX data. I've even seen ones that include hardware handshaking lights. Speaking of handshaking, what handshaking protocol are you using? Interrupting a software handshake sequence can quickly turn a working communication system into a dead system without any obvious external failures.

Good point. In software handshaking, the receiver sends the transmitter a Ctl S (X-OFF) when it wants it to stop sending and a Ctl Q (X-ON) to resume sending. If you can force the transmitter to send a X-ON, it might free it up. I would think if you powered everything down, if this is the problem, it should clear it.

http://whatis.techtarget.com/definition/Xon-Xoff-X-on-X-off-or-XON-XOFF

That depends on the RS232's config. Flow control is not used much these days.

Did anyone load software that might be interfering with WinDNC use of serial port?

Thanks to everyone for putting thoughts on problem.

So far from all suggestion, I come to conclusion that I should look in to RS232 Cable and port settings first, Various test methods suggested are interesting and useful.I will reply some of question posed by some members soon.

Was working and suddenly not....

Easy way to check if it is a cable/connector problem is to connect your second PC at the mill end of the cable using a null modem (crossover) cable and run Hyperterminal correctly configured (same as the WinDNC end) to monitor the data at that end.

You will be able to read the ASCII characters on the second PC's monitor if it, the cable assembly, is working correctly. If you see "nothing' then plug the 2 PCS back to back with a null modem cable to see if the first PC is working, though you did say it worked fine on other devices...

Basic trouble shooting here....If you don't know what's broken find out what is working....

Good luck.

Lots of good advice here already.

You also need to learn the basics of RS232 and how to use a soldering iron to allow you to produce test cables and repair others.

A reasonable Tutorial can be found here, print it off and use it as your Bible. Its not the only one around either!!

RS232_Analyzer_Monitor_Tester_Tutorial

A "solder sucker" or "solder wick" is generally needed to easily re-use a Canon connector. A pin full of solder requires too much heat to get a wire soldered in again....Clean holes help with soldering (they also help with lots of other things too!).....

....but due to often having very soft plastic holding the pins, do not forget to plug in the mating plug/socket to stabilize the pins a bit more and remove heat quicker.

A small adjustable (cheap!) bench vice will hold the plug/socket securely for you at the right angle for soldering......One like this are REALLY cheap and last years:-

A really hot iron and "quick in - quick out" will also help dramatically! You will soon learn as you make mistakes...

I hope this helps a bit further.....

Best of luck and let us know how you get on and what was your problem!!

There is a software program called "Frontline"/ company. This will allow you to listen to and log the communications between the computer and your device. Or any were in between. It monitors ALL RS232 lines.

This will allow to figure out where the problem is.

I have a laptop whose native (integral) serial port works for about 15 minutes but fails when an application requires a continuous 2 to 3 hour data transfer. The fix is to use another laptop with a serial port that can continuously function for 2 to 3 hours.

Over the years I have had PC's and laptops with totally dysfunctional serial ports - dead on arrival.

From these experiences, I have surmised that late model serial RS-232 UART chips were of diminished quality and that the serial port was never actually tested by the PC/laptop manufacturer once USB came into favor.