Serial Port

how do you test the serial port, to make sure that the hardware is working properly.

I need to be able to test DOS machines and window machines.

I am having freezing problems with attached devices and have been told that surges can make a serial port go out, or rather, start to fail.

Any help will be appreciated.

 

I usually just hook up a modem and check that typing in ATH0 and ATH1 into a terminal program change the line status of the modem. That tells you you're transmitting OK. If you see the modem echo back your commands, then you know you're receiving (make sure the terminal isn't on local echo ). This isn't, of course, a thorough test, but it's quick and easy.

 

Thank you so much, I can't wait to go and try this tomorrow, will get back and let you know.

Thanks again.

 

Good one Brummig! I was thinking about this myself and testing an external modem was one thought.
Robin, with Brummig's setup, try running the modem diagnostics in Control Panel>Modems>Diagnostics (tab)>More Info (button). If you have installed a good set of drivers you should get a good deal of information and the PC is communicating well with the modem (although maybe the same as Brummig's commands)

Another way maybe (and could be useful for testing your DOS machines). You should be able to get a serial to serial cable connector (RadioShack?). You can connect two computers together using the serial ports...look in the Start>Help menu under "direct cable connection ". You may have to install it from the Windows CD if it is not installed already. If you can use a Windows computer to connect with, and read the files of, a DOS computer, all should be in order

Matt

 

A computer to computer link has an advantage. But before I go on to that, make sure you buy a crossover cable (a modem uses a straight-through cable). Any vaguely decent computer shop will have all the cable combinations. The advantage of this method is that providing you get a cable with all pins connected, you can turn on hardware handshaking options in the terminal prog and make sure those parts of the port are working. You can also check out all the baud rates. The downside of this method is you do need another PC up and running, and it will take longer. The modem method has the advantage that you *don't* have to worry about communications settings (just pick something reasonable like 9600 baud and no handshaking and the modem will sort itself out), which reduces the chance of your condemning a port because you got a setting wrong somewhere. I have had a serial port die on me, and the modem technique told me in seconds what had stopped working. Usually I discover I had a setting wrong somewhere.

Do you have a DOS terminal emulator? I don't know of any, but Google should help. There may be a DOS compilation of the unix emulator minicom, which (amazingly) is reasonably user-friendly. However, be warned that once it gets out of sync due to a comms error, it stays out of sync.

One further thought, if you have the sort of modem that doesn't click a relay, plug it into the phone line, pick up the phone, and listen!

 

what I am testing, is a POS system that connects to the comm port. The compaint of the users is that the POS is freezing. After checking all settings, wires, jacks...etc I changed out the cpu.

I read yesterday that a serial port going out can cause this problem. Well, of course, after changing out the cpu, if that is indeed the problem, would have naturally resolved the issue.

I have about 60 DOS machines that connect this way, that are about 10 years old....so my thought was, that it very well could be the hardware wearing out.

I am going to test this out when I get out there. I never thought about hooking up a modem. I was hoping that there was a device I could just plug in and read a meter......

I truly appreciate all this help, you know, the DOS creature is still around, and I unfortunatly, see more rj11 jacks than I care to tell you about.

 

I don't know if this will be any help, but it may give someone an idea. (I just had to look up what POS was )

Trying to remember the days of DOS, I know that drivers were "a pain in the butt ". I wonder if you could install a DOS OS onto a harddrive with the appropriate POS software etc(?), so it is fully functional on your test machine. Then, just take the harddrive out an install it into the PCs that you want to test. I THINK DOS runs "standard" drivers that should be compatible with all(?) PCs, so if you changed the harddrive, DOS should run no matter which PC it is on (again, I think).
This would tell you if it is hardware/port problem or an OS/software problem.

Anyway, this may be some food for thought or maybe this is what you do already.
Matt
PS the "test" harddrive could be set up with the appropriate drivers for the external modem.

 

It took me a bit of head scratching before I remembered what a POS is too, so I fully sympathise. I was thinking about this yesterday evening. Robin, I know you said you had checked the external connections, but have you taken the case off and remade all the internal connections? Have you kept the machines clean of dust? The fault you describe is symptomatic of dirty connections. In my limited experience, RS232 ports are generally very reliable, but will die completely if zapped with static (though that applies more to modern high speed ports).

mattman - DOS RS232 comms doesn't use drivers, so in general you are right, you can swap the hard disk over. However, it is something I would personally prefer to avoid doing, just in case there's something about the setup that I don't know about that is hardware dependent.

 

Sorry about the POS statement "Point of Sale" you all know how anal-retentive Acronyms are.......maybe I better leave that one alone.

Because the CPU is located in a kitchen.....I know that the computers are full of "tribbles" as I call them. and grease....this would not surprise me if that was the problem with the connection.

I am working on a larger problem currently and still have not been able to test out the modem. I think that would let me know if the port was valid.

To dang bad there is not a device like a fluke that would do this....

ah, easy way out where are you.

Robin

I love this board. Thank you for your time and your thoughts, it makes the unknown not so lonely.

 

Ok, I have two devices that I have found, but have no clue how to use them.

1. I have a compas microtest. It has a serial test on it. I plugged in a 9 pin adapter, and it asks for a RJ45 cable. I plugged in a Router cable and it still asked for a RJ45 cable......Got excited because I seen the serial test button on the device.

2. You guys got me to thinking. I dug and dug and found a device called a "D25MT RS232 Mini Tester......Well, I attached a gender bender (9 pinF to the com port the other side was a 25 pin...I attached the mini tester to that and the POS adapter to that....yahoooo The cash register worked. Lights came on:

When CPU was powered up

RTS Green light
TD Green light
DTR Green light

When POS program was setup for cash registers to work:

RTS Red light
TD Green light
DTR Red light


When information was passing through

same lights just flickered


Now:

Lights on tester:

CD
DSR
RTS
TD
DRT
CTS
RD


I have no clue what lights mean the equipment is working fine and what lights are bad.....

 

Don't know anything about this device - sorry.

The lights on the other box are as follows:

RTS - Ready To Send
TD - Transmit Data
DTR - Data Terminal Ready
CD - Carrier Detect
DSR - Data Set Ready
DRT - ??? Do you mean DTR?
CTS - Clear To Send
RD - Receive Data.

All you can tell from this is that if they flicker, something is happening, and if they don't, nothing is happening, which is why I don't have one, despite making extensive use of RS232. Actually that's a little unfair - it looks like your system uses hardware handshaking since the handshaking lines are flashing. What it doesn't show is if anything useful is going on.

 

Brumming:

(DRT - ??? Do you mean DTR?)

Yes, sorry for the typo


Well, I guess all I can do is if the three lights are on, all is well. If a light is off, then I am going to assume that the port is dead....oh wait,

I am going into the bios and turn off the port.... and see what happens.

of course, lights went off. I am going to use this as a simple tester....these machines are so old. If port is dead, its dead.

What do you think?