[geeks] Terminal ports

[jodys at helluin.org]

On Tue, Feb 11, 2003 at 12:47:42PM -0500, Andrew Weiss wrote:
> Am I correct in assuming that:
> 
> A. An HP 9000 console port male DB9 is DTE in the same way that a PC 9 pin
> serial port (also Male) is, and that a 9 pin to 9 pin Laplink Serial Cable
> will do the trick?

I can't say for sure in regards to the HP 9000 generally, but I can say
the HP 712/100 715/100 are both DB9 wired DTE. I would imagine that the
machine you have speficially is wired DTE, as not many computer serial 
ports have are wired DCE. A laplink cable is a crossover/null modem cable.
So yeah just a laplink cable would do.

> B. The port on the back of a VT220 is also DTE and would require a DB25F to
> DB9F null modem cable as well?

All you want is the DB9 to DB25 conversion, if you stick a DB9 to DB25 
null modem as so, 

HP 9000 (DTE) -> Laplink cable -> db9 to db25 null modem -> VT220 

it will not work as you've effectivley made a straight cable out of
two null modems. What you want is either

HP 9000 -> laplink cable -> db9 to db25 straight through -> VT220
or
HP 9000 -> straight cable -> db9 to db25 null modem -> VT220
 
Basically all you are wanting to do, in this case, is swap the RX and
TX wires. If you swap it twice your back to where you started. Now if
you are wanting to do hardware flow control, or need some other odd
control line it's a lot more hairy and ugly. But for gaining console
this is fine. Finally if you find that you are having to do this a lot
take a look at building your own adapters and cables using the "Yost"
standard http://yost.com/Computers/RJ45-serial/ which greatly reduces
serial port induced aggravation. Good Luck.

Jody