[CentOS] Need to test serial port connection

[William L. Maltby]

On Thu, 2009-02-26 at 12:31 +0000, Anne Wilson wrote:
> On Thursday 26 February 2009 11:34, William L. Maltby wrote:
> ><snip>

> > As to the OP original question, check BIOS settings and make sure your
> > serial is enabled. Set it to COM 3 and IRQ 4 should work. This would
> > equate to "0" in an *IX system.
> >
> Yes, it says
> 
> COM Port 1 3F8/IRQ4
> 
> It's a long time since I did anything with com ports, and I wasn't expert, 
> then, but that looks right.

It is.

> 
> > Look in your /var/log/messages file. At boot, you should see the device
> > recognized.
> >
> Feb 26 12:12:25 borg2 kernel: serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 
> 16550A
> Feb 26 12:12:25 borg2 kernel: serial8250: ttyS1 at I/O 0x2f8 (irq = 3) is a 
> 16550A

Didn't you say there was only one port? There might be a second on the
main board that is accessible via a header. If it's not hooked up
disable all but the first in the BIOS (later). It's not really hurting
anything as is, but it will free the I/O address and IRQ for assignment
to other devices. But wait until you have things working - I suspect you
have _two_ ports (probably 1 9 pin and 1 25 pin). A second port of 25
pins might easily be mistaken for a printer port. Long ago a switch from
Centronics style to RS-232 style began to become the "standard".
Physically, it looks the same as a serial port, the visual difference
being the "gender" of the connector will be opposite.

> Feb 26 12:12:25 borg2 kernel: 00:05: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
> 
> Is this what I'm looking for?  I don't see anything else.

Yes. That means that all is as expected (i.e. as _I_ expect).

> 
> > Also, Minicom is _easy_ to use and understand. Give it a try. Even the
> > man pages are not difficult.
> >
> Easy when you know how, eh? :-)  I did try it.  I changed it to 
> monitor /dev/ttyS0.  Apart from that, I hadn't a clue what to do.  I did look 
> at the man page, too, but not knowing what I was looking for didn't help.

I haven't used it for a _long_ time, but IIRC there is an interactive
menu system that works with some keystroke, maybe <ESC> key. Look for
that stuff in the man pages and it should be clear sailing.

First, have you set the baud rate correctly? A lot of things used to
default to 9600, but 38400 became common later on. Do the docs for the
unit specify? If so, use the stty command, or in minicom or other
terminal emulator it's method, to set the baud rate to that needed.
Usually these days, no parity check is done so 8 bit characters should
be OK.

Now, since the port is recognized the failure has to be from the port
onward. If the RS-232 9 or 25 pin shell is connected via a cable to the
main board, make sure that the cable connector is connected to the right
header on the main board. Since Linux reported two ports, there should
be two headers on the main board (_if_ that's the method - some ma
inboards have them mounted directly on the main board). If the
header/connector is not keyed, it may be connected backwards. If you
have two RS-232D shells (9 or 25 pin) you may be connecting your cable
to the wrong one.

Moving on, have you been able to verify the cable is good? If you have
an RS-232 patch device with LED's, you can see activity (DTR, DCD, etc.)
by hooking the cable to it. If you don't have one of those, a digital
multi-meter can be used to see if you have expected voltages on certain
pins (+/- 12 volts, IIRC). If you don't have one of those, a plain old
dumb terminal can be hooked up and settings changed in a trial and error
method.

Since they supplied the cable, is it new enough to assume that it is not
damaged? If so, I suspect something easy like baud rate.

> 
> Anne
> <snip sig stuff>

HTH
-- 
Bill