Re: dummy terminal addresses

Hi Lynette,

Some ideas for things to check as follows:


1. The end of the twinax line must be terminated so that the poll from the IBM 
host can pass through each twinax device, bounce off the termination, and then 
return to the IBM host. If you are using twisted pair, the daisy chain 
functionality is in the twinax concentrator itself and each conection from the 
concentrator to a terminal needs to be terminated properly at the terminal. If 
you are using true twinax, all devices but the last one need to be in pass 
through mode and then the last device terminates the chain.

2. You can have up to 7 devices per twinax port. The addressing scheme is 0 
through 6 and all devices need a unique address. If two devices get configured 
to use the same address, a conflict is created that can crash the whole line. 
Printer ports on a 3197 terminal need a separate twinax address from the 
display session. I have seen problems like the one you describe during my 
career when a printer port, with no actual printer, was accidentally enabled 
causing an address conflict.

3. The grounding for true twinax cabling is in the shield surrounding the 
actual wires. In very old cabling, it is possible for the shield to break 
somewhere in a cable causing a short to occur. Sometimes everything will 
continue to work correctly even with a short until a device is removed or 
installed. The minor jostling of the damaged cable will allow the short to 
prevent the whole twinax port (or sometimes a portion of the devices on the 
port) from working until the damaged cable is located and replaced.

4. Twinax devices are supposed to respond when contacted by the host. Sometimes 
a hardware failure occurs on a single device, which causes it to stream answers 
onto the twinax link (effectively talking all the time filling the bus up with 
data <twinax is only 1 Mb/sec> so that no other device can function) causing 
some or all devices to fail. The line will typically remain down until the 
device is located and removed. You can test for this failure by powering off 
all devices and then powering on a single device to see whether it works. If 
yes, move to the next one and continue powering devices on one at a time until 
you find the one which causes the line to crash.

HTH

Best Regards,

/Paul
--
Paul Tykodi
Principal Consultant
TCS - Tykodi Consulting Services LLC

E-mail: ptykodi@xxxxxxxxx



>date: Tue, 14 Feb 2006 09:24:03 -0500
>from: "Lynette Chronister" <Lynette.Chronister@xxxxxxxxxx>
>subject: dummy terminal addresses
>
> Ive found myself in a situation.  We no longer carry support on our
> remaining six 3197s.  Im having issues getting them to connect, and
> cant ask our Business partner to come and take a look...
>
> chain of events:
> Tuesday:  Warehouse decides they dont want one of the dummy
> terminals at their workstation, so they disconnect and remove.  They
> say everything else was working okay.
> Wednesday:  power blip.  All terminals will not respond.
>
> Ive tried everything i can think of, its been TOO many years since
> ive dealt with them, and i had limited experience back then.  The
> naming convention is DSP##.  I remembered how to print the  device
> addresses (PRTDEVADR), but it is not helping me.  There are 15
> devices listed on that controller.   I cant seem to figure out on
> the terminal itself what port it is assigned to???  The series of
> numbers at the bottom are confusing to me.
> I know that Cmd23 sets the address(switch).  i have series of
> numbers on the bottom of the screen..  ex:  10    4   0    3 (i blve
> the 3 is the switch in this case).
>
> Questions:
>
> I sort of remember if the terminals were daisy chained that if the
> first goes down, the rest behind are dead as well???
>
> If that is the case, them removing the terminal made the rest go
> down?  why not right away?  i replaced that terminal where it was,
> its still not working?
>
> I thought that if terminals were 'daisy-chained' that meant they
> were defined on the same port?  Two could possibly be on the same
> port, but not all 4. I have another terminal, a 3179 on another
> controller, working fine.
>
> It seems to make sense in my mind that if they are all down, there
> is a problem in the line?  I ruled out a problem with the
> controller.  There is a printer defined on that same controller, and
> that is working fine.  I have a tester (antique looking thing, it
> has a switch to set to 1, 0, or 2 and two amber lights and a green
> light)...  Im not even really sure how to use this!  How can i test?
>
> ive tried varying off all devices, varying off the controller and
> bringing them back up.  I can access the setup screen on all
> machines, does that tell me they are not dead?
>
> There have been no other changes on the system.  We do a scheduled
> re-ipl Sunday nights, which completed normally.
>
> Any suggestions would be so appreciated!!!  My whole warehouse have
> been using the same pc to access the system for 5 days now!!
>
> Lynette (Nettie) Chronister
> Programmer
> Phoenix Mecano
> Frederick, MD  21704
> 301-696-2145

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