[CentOS] Need to test serial port connection

[William L. Maltby]

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.

Look in your /var/log/messages file. At boot, you should see the device
recognized.

Also, Minicom is _easy_ to use and understand. Give it a try. Even the
man pages are not difficult.

> 
> Phil
> <snip sig stuff>

HTH
-- 
Bill