[time-nuts] Thunderbolt serial connection - null modem or straight through?

Matthew Smith matt at smiffytech.com
Tue May 20 17:59:58 EDT 2008

Quoth Hal Murray at 2008-05-21 06:06...
> My standard setup for debugging RS-232 cabling is one of those gizmos with a 
> handful of LEDs.  They are green for one polarity and red for the other.  
> Mine is actually a 25 pin version so it lives with a pair of 25-9 adapters.  
> I use it with a straight-through cable (extension cord) to position it out 
> where I can see it.
> Connect it to one side.  Look at the lights.  Then disconnect it from that 
> side and connect it to the other side.  Different LEDs should light up.  If 
> they overlap, you have troubles.  If both sides light TD or RD, you need a 
> null-modem type cable.  (or to remove the one you are already using)

A good breakout box is an essential tool for anyone working with serial 
links.  (At least I think so!)

My old 'Interfaker' has both male and female DB25 connectors on either 
side and a switch for each line.  The switches mean that any line can be 
broken and re-patched using rows of 0.1" sockets and little patch leads. 
  Typical use is when you need to reverse RXD and TXD - just flick the 
switches off for those lines and hook in the patch cables.

I started using these beasties back in the days when I was running a 
load of Wyse terminals off an IBM6150 (RT/PC in the USA).  That's before 
I ever SAW a Pee-Cee; oh happy days...  Thing is, even in this day of 
serial to USB adapters, I wouldn't let anyone take my old Interfaker away!



Matthew Smith
Smiffytech - Technology Consulting & Web Application Development
Business: http://www.smiffytech.com/
Personal: http://www.smiffysplace.com/
LinkedIn: http://www.linkedin.com/in/smiffy

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