[CentOS] Need to test serial port connection

[Anne Wilson]

On Thursday 26 February 2009 11:34, William L. Maltby wrote:
> On Thu, 2009-02-26 at 06:14 -0500, Phil Schaffner wrote:
> > On Thu, 2009-02-26 at 10:17 +0000, Anne Wilson wrote:
> > ><snip>
> > >
> > > There is just one serial connector on the computer, so I set it to
> > > monitor /dev/ttyS0.   Either that is wrong, or communication is
> > > failing. I've been told to try minicom to monitor it, but I'm not
> > > familiar with minicom (or any similar app), so again, I may be wrong in
> > > the way I'm trying to use that.  I was told that unconnecting the
> > > device, then re-connecting it should give me a raft of output to the
> > > terminal - I saw nothing.
> > >
> > > Could someone please give me idiot-level instructions on how to tell
> > > whether I'm connecting to the correct port, or whatever other
> > > information I need?
> >
> > Anne,
> >
> > Are you sure the cable is correct?  I recall in the past having trouble
> > with an APC UPS that required an oddball RS-232 serial cable before it
> > would communicate.  There were different variants available and only one
> > would work.  Posting details of the brand/model of UPS involved might
> > get better help.
>
> OTOH, if the manufacturer has any common sense, at worst they'll require
> a "standard" (NOT!) null-modem cable. At best, they'll have
> circuitry/software on-board that accepts either a straight-through or
> null and adapts itself.
>
> Being an _old_ telecom guy from way back, I prefer what was called a
> symmetrical null modem fully configured. From memory (and therefore
> suspect)
>
> Pin---->Pin
>   2       3
>   3       2
>   4       4
>   6       6
>   7       7
>   8      20
>  20       8
>
> Some also do 5 to 5.
>
> However, a 2-3 cross and DTR and DCD high is all that really is needed.
>
> Google for RS-232 will get you a ton of stuff.
>
> 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.

> 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
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.

> 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.

Anne